Dude what blows the theory out of the water that we need to play an extra man in midfield because we lack players there is the team with the best midfield in the world - Barca play with a 3 man midfield or is that because they are weak and lack the players to play with a 2 man midfield?
Chelsea play with a 3 man diamond and Pool play with 2 holding midfielders and Gerrard coming from deep.
So in all cases a 3 man midfield is required not because we lack the players.
United still revert back to a 2 man midfield in the easier games they play, which is a difference. The other teams you mentioned set up similarly regardless of who they're playing. Look at our league games this year;
Started with 4-5-1:
Chelsea H - necessary
Bolton A - Rest Rooney before Munich tie, no Owen or Macheda available
Liverpool H - necessary
Wolves A - Rest Rooney before Milan tie, no Owen or Macheda available
Villa A - necessary
Arsenal A - necessary
Birmingham A - a bit of an odd one, Berbatov wasn't available, and Ferguson didn't like to use Rooney and Owen together? Even Diouf came on ahead of Owen. Didn't pay off anyway, 3 shots on target all game.
Started with 4-4-2:
Fulham H
West Ham H
Everton A - lost that 3-1, and we were even up against an Everton midfield 3. Beat them comfortably 3-0 with a 4-4-2 at home though, probably thought it would be enough to get by
Portsmouth H
Hull H
Burnley H
I would guess we'd have played 4-4-2 against Wolves, Bolton and possibly even Birmingham if we'd had the right players available for it, and that for the most part shows that we'll still play 4-4-2 when at all possible. We've even needed to stick three in midfield against a two man Bayern midfield at home!
You could argue that these remaining 4-4-2 games are some of the last we'll see, and you could be right, and in that case I don't think Berbatov will be useful enough for us to keep. But I really can't see us setting up in a 4-5-1 against lower table teams who are likely to combat us by packing everyone into their defence, and these are the kinds of games where Berbatov can give us an extra dimension. Like I said earlier in the thread, these are the games where Chelsea, Liverpool and Arsenal have dropped points time and again, and this season we've been far more efficient in them.
Berba as you mention is not a flexible or adaptable player its 4-4-2 with him or the highway but the game at the highest level has adapted so much that 4-5-1 or 4-3-3 is the future. Berba is the past - no top side will ever buy him and we cant play him in big games.
Berba is a relic of the old formations of a link man in a 4-4-2 - this has been shown at the highest level to be easy to combat.
So don't use it at the highest level! Use it at the lower levels where we'll easily win the midfield battle, but may have a bigger problem breaking through a crowded defence!