For that matter, in 2004 the Republican ground game was much stronger than the Democratic ground game, which was probably critical. I don't see anyone claiming that the Romney ground game is better than the Obama ground game.
If the election ends up turning on the ground game, then Romney will lose and likely lose badly. His performance in the primaries indicates that he places little importance in a ground game, tho when the rules such as those in Virginia with its complicated ballot requirements required he build at least some ground game, he was able to. So it's not a lack of ability to engage in the ground game, but rather a feeling that he is better off focusing on other campaign aspects.