Benitez can hardly be surprised if there is this kind of speculation as to why Aquilani isn't featuring. I don't believe it is as simple as match fitness seeing as he has played Gerrard,Torres,Johnson,Benayoun,Agger etc throughout the season when they haven't been 100% fit. I can't help think that he simply doesn't want to break up the Lucas-Mascherano partnership because he has convinced himself that it works fantastically.
Interestingly one of them on 5 live (Green or Pleat can't remember) said that they thought that Gerrard would move into midfield next to Mascherano and Aquilani would play behind Torres when he came into the team??