The attempt to only plead guilty to some charges in interesting. He's apparently been told that if he pleads guilty to the gambling charges he could be more harshly penalized by the NFL. And he doesn't want to admit to taking part in killing the dogs for legal and
PR reasons.
The prosecution has been very skilled in the way they've handled this case. I'd expect them to tell Vick's lawyers that he has to plead guilty to more than what he's offered to so far, or they'll file additional charges and/or recommend a longer sentence. But the brinksmanship on the deal opens the possibility of a trial actually happening.