He didn't play at the end of the Orlando game because he sat down in foul trouble, and then did not come back because Davis was very effective on both sides of the ball, and Doc didn't want to mess with it. I think it's kind of the same thing as when Doc leaves Wallace in there, he does not want to have someone in (or someone else, other than Rondo), who cannot make defenses pay for leaving him wide open from 15 feet (or deeper), but in yesterdays case, it was Davis, because he was playing much better than Wallace.
This is especially important against the Magic, since if you put Perk in there, it gives Howard carte blanche to roam around the paint, and block shots, but if he has to cover someone like Davis, KG, or Wallace, it makes him at least take an extra step or two out of the lane.