Gamesmanship in my opinion doesn't only happen on court. It also happens off court. You have to take care of what you say and be a gentleman. So Federer and Nadal are balanced out. Federer behaves perfectly on court while he's an arrogant prick off it. Nadal behaves suspiciously on court while he's the perfect gentleman and gracious loser off it. Why is one better than the other?
I disagree. There are no stated rules tennis, or perhaps most, if not all, sports, mandating players to be polite to each other off-court. However, there are tons of rules put in place to police on-court behaviour to ensure fair play as far as possible. Tennis players are not obliged to be nice to each other when they're not playing a match, but they are obliged to follow the stated rules of the sport that they choose to play. Whatever they choose to say off court is their own business, and it's entirely on them if they choose to say things that make themselves look like sore losers, etc. But it's not at all up to them to break the rules of the game.
And of course, tennis is traditionally a gentleman's sport, and thus players are expected to behave like gentlemen - on court. Off court, again, it's really their own problem. Mouthing off at opponents in post-match interviews makes a player look like a sore loser, but it's nothing compared to time-delaying tactics employed during a match with the intention of disrupting your opponent's rhythm, or even throwing a hissy fit when you're losing a match.
Also, while I agree that Rog isn't always the most gracious loser, I think Nadal has had his moments as well.