I think Chelsea should focus more on trying to qualify for the Champions League than winning the league.
Yeah it's in ManU's "hands" but based on your guys' definition, the title is always in the "hands" of whoever is in first place. Chelsea and Liverpool obviously have a "say" because it is possible (though unlikely) that the title race could be extremely close between ManU and Arsenal, and if they make ManU drop points, that could be the deciding factor.
But even if ManU does drop points to Chelsea or Liverpool, there's no way that Arsenal will get any points at OT and that will ultimately be what decides the title. I bet ManU will finally pick up in form like they always do in the latter part of the season and I think they'll win 11 out of the next 12 games. I think the one game they won't win is the one at Anfield, I bet Liverpool gets a draw out of that one. Maybe, just maybe, Chelsea fights to the draw in one of the games, but I don't think that'll happen. Other than that they should win the rest.
I think Chelsea is in serious danger of not qualifying for the Champions League. Tottenham has been in great form and Chelsea has to play Arsenal once and ManU twice. So if that happens, what happens to Chelsea? Obviously Ancelotti leaves, but will there be some serious house cleaning? Who will leave? Drogba and Anelka at least. They'll need new signings, and who will be the manager? I can't think of anyone good that will be available at the end of the season (other than Benitez). Maybe they could get Deschamps to come? And what about getting Mourinho back? If Roman begged him to come back and offered him total control, would he do it?