That's very true, but you can do that while playing with friends or farming kills as well. You can use the farming method to knock out all the game types you don't like to play while you actually play and win in the ones you do enjoy playing, that sort of thing. It's more of an accompaniment than the primary method of boosting.
100% retail - Lego Batman, Lego Harry Potter Years 1-4, Lego Star Wars TCS, Batman Arkham Asylum, The Godfather (1250), Resident Evil 5 (1000), Oblivion (1250), Dynasty Warriors 6 Empires, Fallout 3 (1550), Avatar TLA, Marvel UA, Marvel UA 2 (1000), Left 4 Dead (1225), Assassin's Creed 1+2, Sega Megadrive UC, L.A. Noire (1200), The Saboteur
100% arcade - Gunstar Heroes, Pacman CE DX, SSF2T HDR, The Dishwasher Dead Samurai, DR2 Case Zero, Banjo Kazooie, Dash of Destruction