Umm no, the major problem with epubcheck is that all it checks for is the conformance of epub with various DTDs. In the real world, conformance with DTD's is by far the least important of all checks you could possibly perform. The only reason that epubcheck exists at all is that it is trivial to code.
And yet, the existence of epubcheck convinces endless scads of people that their epubs are going to work as they intended, just because they pass epubcheck. I would have been so much happier if trivial had been prepended to epubcheck. But then no one would use it and then how are we to give people a warm and fuzzy feeling that their epubs are A OK and going to work forever.