The fact that their message and their focus isn't geared towards everyone is besides the point. Much like colour is colour, usability is usability.
Sorry for being harsh, this is just my opinion and isn't meant as a slam in any way :)
(no 'slam' taken.. differences of opinion are great).
Red is red, and always red. But usability - there;s not really a one-size fits all, is there? the AOL browser needs a different type of GUI from this page I'm looking at now, because you can assume different interests, knowledge, familiarity with web design issues. Because the audience is different, you can assume different usability requirements.
btw: we can continue off-list later if you like.. gotta go and cook my kids' dinner...
If you are looking to impart information, then usability and accessibility are important, absolutely.
Sometimes, I want to read the W3C specs, an essay or a news story. In those cases, I don't want to have to wade through incomprehensible navigation and wait for things to download.
Sometimes, I want to lose myself in a site and just marvel at the wonder of it. I want to push buttons and see what happens; I just want to play with a site.
Usability isn't an empirical issue, it can't be measured. Jakob is talking out of his **** there. Usability requirements are usually worked out from use cases: what does the visitor to the site want to do? If they want news, they have one set of usability requirements; if they want to play with Flash toys, they have another.
Accessibility is another matter. I code to standards, I write standards compliant templates for friends, I an currently working on a site for a government agency which requires that the site comply with WAI-AA guidelines. Yet, I can't esacape the conclusion that accessibility should not be the overriding concern of everyone making a website. Your Flash developer/designer is setting out to make something that fulfills a certain need to make something interactive, playful and/or mystifying. Folks, SVG just isn't even close to being capable yet. So what if it's text based, how is a screen reader supposed to cope with:
There are certain people who just can't use certain things. I don't see people getting so up in arms about DVDs without closed captions or roller-coasters that don't allow people below a certain height to ride.
<linearGradient id="pencil" x1="0%" y1="0%" x2="100%" y2="22%"
<stop offset="0" style="stop-color:#ffe401;stop-opacity:1"/>
<stop offset="1" style="stop-color:#e0c858"/>
If you are creating something that is a visual experience, then you can't hope for it to be accessible to all, the same way a painter can't. Do you really think Joshua Davis, for example, wants to exclude people from seeing the things he makes? But he knows Flash. The problem (such as it is) lies with Macromedia.
I'm jumping rather late on this thread but I would say ONE of the things that makes a website usable is making it so most users instictivly know how to use it. This consists of making the navigation clear and obvious, making multiple methods of navigation and keeping the navigation in a constant place.
A lot of other things contrubute to making a usable site but that is one of the main ones in my opinion.
Easy to use
A Liquid site, so it will fit into all browsers.
Less client arrorgance.