Of course not... just trust him though, he knows.
However, specific to this bug; it was filed by a blind user who has just spent 2 years working directly with the Drupal 7 community ensuring that Drupal 7 is significantly more accessible to both content recipients, as well as content authors. He has worked on specific patches within D7 core, which have been committed, and so whether he is an "expert" or not is not relevant. He is a blind user with a close and clear understanding of authors and users, and specifically of blind authors and users such as himself. Or are those credentials not enough to 'allow' him to make this statement:
"As I explained above, the author is setting a poster. There is therefor a
visual image on the page, it conveys meaning (or at least has the ability to
convey meaning), I want the meaning as much as someone who can see the image." - http://www.w3.org/Bugs/Public/show_bug.cgi?id=10642#c8
Expert or not, what about this request from a blind person is hard to understand?
An example from the accessibility sphere is the "longdesc" attribute. If you ask users what they want in terms of images, they will frequently claim that what would be most useful for them is a way of getting longer descriptions of what images are. However, if you actually look at how AT users interact with the Web, it becomes abundantly clear that this isn't true: by and large they never actually seek out longer descriptions of images; indeed, they generally don't find any need to even know that there are images.
This kind of binary thinking is, frankly, bull-feathers. There are many types of users, and there are many types of blind users. An interesting point of distinction is between those who have been blind from birth, and those who lost their sight later in life. For those blind from birth it is often true that rich visual descriptions are often not that relevant, as they have nothing to compare those descriptions against. But for those who have lost their sight later in life, they do have the visual memories to draw upon, and those users often do appreciate good descriptions. Mr. Hickson claims that "...they generally don't find any need to even know that there are images." This bold assertion is based upon what, exactly? Is there a study, survey or other unbiased source as the foundation of this claim? If a graphic images does convey some critical information, then blind users want to know that too: if it is a diagram from last week's Computer Science lecture, then wqho says it's not important? But broad sweeping statements make great sound-bites... and Ian Hickson is actually very good at that kind of manipulation, he even writes about it and practices it: http://ian.hixie.ch/bible/handling-people
The net result of all this is that when a user or author reports a bug, one has to be very careful to actually examine whether their request is actually sensible or not. The true experts are the ones who can tell the difference.
...the subtext being that he knows more than actual blind users what blind users need and want. After all, he's a 'true expert'. Am I the only one who reads this tripe and shake my head in disgust?
Another common mistake is to view the Web as primarily a visual medium, which must then be adjusted to work for AT users. This is the kind of approach that leads to "bolt-on" accessibility and poorly-devised features like longdesc="", summary="", or the aforementioned posteralt="". I feel this kind of approach basically is treating disabled users like second-class citizens.
"I'm confused. Why would you (a blind user) want to know what the poster frame is? How does it affect you?" (Ian Hickson - http://www.w3.org/Bugs/Public/show_bug.cgi?id=10642#c7)
In other words, because you are blind you don't need to know what this is. Every sighted person does, but you - blind person - you don't. Trust me, it's not important...
(and Mr. Hickson dares to lecture on creating second class citizens?)
The right way to design a device-neutral, medium-independent, universally accessibly markup language is instead to start from the standpoint of each kind of user — partially blind, hearing-impaired, having reduced motor control, speaking only English, etc — and to ensure that each feature makes sense in that context.
So let's examine this.
HTML5's <video> element will also allow an author to specify an image, any image (any image) as the 'poster frame' - a graphic that fills the same region as the intended video playback 'box'. Upon activation of the video, the image will be replaced with this new content. Conceptually we now have 3 things: a region that contains content within a web page, a graphic file (.jpg/.png), and a video (.ogv/.webm). From the perspective of what is sitting on the server, there are 3 files: .html, .jpg and .ogv. To ensure "medium-independence" we need to ensure that all of the visual elements used on a web page have an equivalency for those who cannot see. It should not matter that based upon a user interaction one visual element is replaced by another: both visual elements require descriptions for the non-sighted. It context, doesn't that make sense?
Apparently not to Mr. Hickson. He thinks that the still image is meaningless, it has no need of description because what is important is the video, not the image. Says who? If the image is not important (or stands the possibility of being important) why does HTML5 even allow the author to specify an image? Why not just always use the first frame of the video, and provide a textual description of the video for non-sighted users. The moment you allow authors to specify an image as the poster frame you've opened the door for the author to use an image that may have absolutely nothing to do with the video (http://www.cineshoppe.com/graphics/ex0065.jpg alt="box of popcorn") Not allowing the non-sighted to know what this image is makes them second-class. Deciding for them that knowing or not knowing is immaterial to them is the worst kind of condescension I've ever encountered.
If you instead apply "cargo-cult" thinking, treating users of ATs as second-class citizens, you might come to a different conclusion: you would look at the visual page, think "Well there's an image there, and all images need alternative text", and you would ask for a posteralt="" attribute. But if you think of the AT users as first-class citizens, you would never even notice the poster frame.
Remember, this request came from a blind user. No matter how much Mr. Hickson wants to argue this away, the reality is that an informed blind user/developer/engineer didn't see an image there - but he knows it exists and wants to know about it more - a not unreasonable request. A truly Universal Design pattern would account for this, and frankly is a problem not that difficult to solve... except Mr. Hickson as editor didn't think of it first, and when it comes to "accessibility experts", well he knows only too well that he's smarter than a boatload of them, so...
The up-side at this time is that this inequity and inequal treatment of non-sighted users is now a W3C Issue - a point serious enough to block HTML5's progress to Last Call until resolved. Hopefully despite Mr. Hickson's myopic view of what is and isn't required for Universal Access, we'll get this right.