Le blog personnel de Joe Clark | Time to call bullshit on Six Apart:
Movable Type and TypePad, like all blogging software, fail to meet the Authoring Tools Accessibility Guidelines (ATAG). The difference here is that Six Apart has known about it for years and claims to care, yet has done nothing.
The short summary: it's not just a tool's output which has to be accessible, the tool itself needs to be accessible (most blogging tools use a web interface). Clark's particular beef is that Six Apart claim their tool is accessible, when it doesn't meet the relevant guidelines.
Clark observes that nobody, in fact, complies with ATAG and plenty of companies don't even comply with WCAG... for example, Google gets no quarter for their failure to Do Good:
Google doesn't give a shit about accessibility or Web standards. Gmail is still inaccessible (see later complaint), despite one developer's promise to fix it. I challenge you to find valid code on anything Google produces. Anyone who has been reading this blog for any length of time will recall my occasional rant on that topic, particularly given Google's mission statement including efforts to 'make the world better'.