It’s unfortunate that the WhatWG made a unilateral decision to go Last Call with HTML5 at WhatWG, as HTML5 is far from ready for Last Call at the W3C.
Supposedly the reason it went to Last Call at the WhatWG is no bugs in the WhatWG database. Considering that there are significant bugs and issues at the W3C, one can only assume that concern about quality is not as strong at the WhatWG as it is at the W3C.
There are also more people questioning decisions, issuing proposals for change, and submitting bugs at the W3C. If one were suspicious, one could imagine the HTML5 editor made this move to assert some form of control.