The basic difference between a technology that is accessibility supported and a technology that is relied upon. But the scope of both terms is wider and more complex that a single-line definition.
At this point you will probably wonder which web technologies are accessibility supported and which are not. And the answer is… nobody knows, not even the WAI! Now, the consultancy best phrase: ‘it depends’. How is this possible after 5 years of WCAG 2 developing? Well, some reasons for this vagueness.
Let’s assume that nobody knows which technologies are and aren’t accessibility supported. Now what? Well, the WAI has tried to bring a definition, not very clear, but a definition after all:
a Web content technology is “accessibility supported” when users’ assistive technologies will work with the Web technologies AND when the accessibility features of mainstream technologies will work with the technology.
Remember these categorical clauses? ‘Don’t do your web in Flash because it will not be accessible’ or ‘Avoid PDF, because a blind person won’t be capable to read it’. Industries participant in the redaction of the new guidelines have adopted a tougher line protecting their products from legal barriers. So that’s why there is no mention to which technology is accessible and which not, because it depends on the way that they are used. E.G. You can use plain, strict XHTML but it is not well formatted, it wont be accessible. But if you create your website with Flash and all the accessibility features on, it will be accessible.