The definition of "accessible" could be pretty broad. It doesn't have to mean what you have in mind. As I see it, is this WYSIWYG editor making the web more accessible to laypeople who don't know HTML, CSS, etc.? Definitely.
The tag line did not contain that exact phrase. It said "make the web accessible". Try googling "accessible definition"? Also, they seem to have since changed it to "easy to use", so the intention is clear. If you want to be offended by their use of the original meaning of "accessible", by all means.
EDIT: Okay I retract the "did not contain that exact phrase" part; I thought you were talking about their company's tag line. Anyway, feel free to be mad at the word choice.
