Add: Careful attention is paid to accessibility, including the use of ems rather than pixel based font sizes and use of HTML elements as they are intended, such as headers.
A modern web site would use HTML 4 strict. HTML 5 is still in draft and therefore only really available for testing as everything in it could be completely different tomorrow. Also with XHTML there are still to many people using IE8 and earlier which don’t support XHTML to be able to use that yet - although it should be usable long before HTML 5 becomes a standard.
A bloated library for those who are trying to take the easy way out by not learning enough JavaScript to do it properly for themselves. Therefore not necessarily an indicator of a modern site since if someone associated with the site does have a moderate knowledge of JavaScript they would be able to use JavaScript that is just as modern as that in JQuery but with about 40k less code.
Or better yet use a server site stats program with the server log so as to count all visitors and not just those with javaScript enabled.
If we want to characterize the modern web it can be classified in following areas -
It should be unbiased, i.e it is operable to all of platforms. (One web for all)
Flexibility
Simplicity and intuitive
Perceptible
Be preventative
Tolerable
Effortless
Accommodating
Consistent
Ability to Handle real world challenge
That’s right. It’s only ie6 that struggles to resize px fonts. There’s nothing wrong with using pixels for font-size these days.
You’re list isn’t too bad, I would put these at the top of the list as the most obvious ways to tell a modern site.
The site is built in a way so that it loads quickly, lean HTML, Minified & compressed assets.
The site works well with mobile devices (responsive CSS)
CSS3 is used in preference to images
clean URLs
Use of appropriate libraries to simplify the code.