Not to be flippant, but there's a blog about this:
http://www.allaccessblogging.com/

My own experience is limited, but I think it's true that blog accessibility
is controlled more by the theme applied to the blog than to the engine
itself.  WordPress has a good reputation for accessibility, but you can find
themes for it that are inaccessible.

All 3 blog platforms you mention have lively communities that can answer any
question you have.  I've found the people at wordpress.org to be friendly
and well-informed every time I've needed something.  You could start here:
http://wordpress.org/tags/accessibility

***
Jim Tobias
Inclusive Technologies
+1.908.907.2387 v/sms
skype jimtobias
 

> -----Original Message-----
> From: Prof Norm Coombs [mailto:[log in to unmask]] 
> Sent: Saturday, May 30, 2009 3:54 PM
> To: [log in to unmask]
> Subject: Re: AQcessible Blogs, Podcasts, Wikis etc.
> 
> I don't know.  I avoid blogs.
> 
> I have a memory that wordpress was good but that may have changed.
> At 11:53 AM 5/30/2009, you wrote:
> >Hi!
> >
> >I've been asked to participate in a project and I have to 
> choose a blog 
> >site from Google, Wordpress, or Typepad. Are any of these more/less 
> >accessible than the others? I need a reply before midnight 
> June 1, if possible.
> >
> >I know EASI teaches an online course, but its one I haven't had yet!
> >
> >Mary Jane Barnett
> 
> 
>   . . . . . . . . . . . . . . . .
> 
> Norman Coombs [log in to unmask]
> CEO EASI Equal Access to Software and Information phone (949) 
> 855-4852 (NOTE pacific time zone) ****READ ABOUT THE DICK 
> BANKS MEMORIAL SCHOLARSHIP:
> http://easi.cc/scholarship.htm