I've never heard of any company being sued for lacking accessibility. I can't believe Target was sued for that. Anyway, I think it's very important to conform to
web standards. Not only will your website be (1) faster to load and (2) easier to modify, but it will also be able to be viewed through wireless technologies, the blind, and so forth. I would really recommend coding in at least XHTML Transitional if not XHTML Strict.