A little thing called rotation, though I grant you it's understandable as a fellow Villa fan, you wouldn't have heard that term recently.
Either way, wouldn't we have Delph available in that kind of area, when he's fit anyway?
Yep. I think if we had Petrov, Ireland, Reo-Coker and Delph as our four central midfielders then we'd have some good options for the season. Probably keep Sidwell til January until Delph is fit again.
Then you could also use Young or Downing (or Ireland too) in the number 10 role if we were going to play five in midfield.