Let me suggest that there's a more fundamental issue here.  In order to
design web accessible web pages, a web designer must have an idea of the
capabilities of the person accessing the web page.

The standard suggested solution to this is to write for the lowest common
denominator.  I would like to suggest that that is not a reasonable
solution, and is becoming more unreasonable as the available tools get
better at dealing with sophisticated html code.  Why should I go to the
trouble of building in an interface that's not needed by my non-disabled
users or even by my disabled users using the correct software?  Do I have
any moral responsibility for the software that a user decides to buy?  Is
this any different that arguing that I have to provide a telephone interface
to my web site for disabled users who choose not to buy a computer?

I would like to suggest that there is a better solution to the problem.  We
need to find a good set of software including browser, screen reader and
whatever else is needed, buy the rights to it and put it into the public
domain.  In effect, replace lynx as the freebie that we know everybody can
afford with something with a little more horsepower.  Once this is done, any
designer who creates a page that runs under this configuration and meets
some basic standards will satisfy accessibility requirements.

There are, of course, a couple of problems with this.  The first is what
goes into the package.  The more we put in, in terms of capabilities, the
easier life becomes for the designers, but the harder it will be to create
the package.  The second is identifying and dealing with all possible
accessibility problems.  I can tell you that most people who I talk to who
don't normally consider this area, regard "accessibility" as short hand for
"access for the blind".  There will almost certainly be some areas that no
software is going to be able to deal with and we're still going to depend of
standards and guidelines.

Another issue is who's going to pay for the rights, and also for updating
the package as developments warrant.  Ideally it should be the web sites
since they benefit by having the work of assuring accessibility simplified.
However, it's hard to see how we would actually collect from them.  More
likely it would be the government which, since the 508 standards came into
effect, has a motive to try to standardize the process of achieving
accessibility.