Jamboree: An Englishman sez:
"I don't understand one part of the game, when Black had a Rook on h2 and numerous chances to snatch the g2 pawn (e.g., after 40.Bd7). Why didn't Nakamura take the pawn?"
I believe the reason is because Aronian was ready to spring a diabolical trap!
If 41. ... Rxg2, then white plays
42. Rh1! and suddenly black's rook has no flight squares! White is threatening simply Kf1 or Bh3 and the rook is lost!
No black king or pawn move does anything to rescue the rook, so his only hope is something like 42. ... Nf5, but then white just goes 43. Kf1 anyway, and it looks like black either has to sac the knight to save the rook with 43. ...Nxe3+, which leads to a lost endgame, or his only hope to hang on to the material which would be then 43. ... Rg4, but that leads to a terribly cramped position for black, with the knight pinned and the king protecting the knight, and it looks like white could then go 44. Rh8, the swing over and nab the undefendable a pawn, while black struggles to untangle his knot of pieces over on the kingside.
The problem then for black is that if he tries for counterplay with 44. ... Rh4, 45. Ra8 Rh1+ 46. Ke2, now white is threatening to win the knight with 47. Ra6+, and black has to deal with that problem instead of playing the hoped-for 46. ...Rb1. So then white will win the a-pawn uncontested, and will easily usher the two connected queenside pawns down the board, as black's king and knight are way offsides and won't be able to stop them.
So, THAT's why Nakamura didn't play 41. ... Rxg2?