To be fair...
Getting Joomla to validate XHTML and CSS through the W3C Markup service and Section 508 through Cynthia isn't too onerous a task, depending on the template you choose to implement. A bit time consuming, to be sure (my... uhh... "hobby" at the minute is validating a few oldie-but-goldie templates
), but not a killer. That's why I would recommend creating your own template, time and skills permitting
WAI, on the other hand, is a complete bummer for anyone who isn't to some extent "adept" with php (and that ain't particularly me!). Even Joomla! itself doesn't output valid code for WAI without some core file hacks. Or, at the very least, doing some stuff "the long way 'round" (e.g. inserting an image into an article - "Lemme hear ya say HSPACE! Yeah!"
). And then you've got to factor in the wide range of 3PD stuff that's available - and probably essential for your site - a lot of which does not even generate valid XHTML "out-of-the-box".
So, yeah... it can be a struggle, but for me - it's worth it. Oh, and as for
at least as good as the existing sites (which should be accessible) like RNIB
Their site doesn't validate WAI. Which just goes to prove what I've thought for a long time, now. The "Validation Grail" is a bit like a penalty shoot-out. Take your eye off the ball for a split second and you've just kicked a divot into the net.
BTW - Check out A8E Joomla - an "Accessible Joomla!" package. May get you off to a flying start!