When I've watched Roma, in the 10-12 matches that I have, this guy was always giving his all.
I watched those matches too. Those were the matches against the better teams.
I also watched many matches where he was really bad.
Overall, he did shine in some important matches and showed leadership, so he deserves to be in this poll.
Especially since the competition is far from impressive. The quality central midfielders or DMCs (like Pirlo, Gattuso, Melo, Sissoko, hell, even Montolivo or Zanetti) had even worse seasons than De Rossi and if you think about it, not even more than 3-4 players deserve to be in this poll ahead of DDR.
The above mentioned players, like Pirlo or Melo, had very bad seasons. Some others like Gargano, Galoppa, Morrone etc, were inconsistent as hell and never impressed. Cigarini was more of a bench player. Isla was average. Almiron was ok, but even more inconsistent than De Rossi. Marchisio was mvp on some 4-5 matches and showed great potential, but was he really better than De Rossi?
So only the Inter duo, Pizarro, Liverani and Palombo might have a case against De Rossi.