Again I'd put U2 at the top for staying on top of the game, staying together and continuing to write together, was it their meteoric rise of the 80s or odd experimental success of the 90s? No, but NLOTH is a step in a new direction, and they're the untouchable live success, some of these other artists might have sold more singles downloads, but those numbers don't stack up against U2's billion dollar decade of touring.
RH of the 90's I love, the RH everyone else now loves of this decade? Way too into their own heads for much enjoyable listening personally. Kanye's a hell of a mixer/producer, but he's not much of a rap lyricist. Springsteen's had some great SONGS this decade, one masterpiece of an album (The Rising) and another pretty great one (Magic), but he's not exactly winning new fans across generations this decade. Arcade Fire, no thanks, some fun songs here and there and a legion of pretentious fans, regardless of your love for them indie kids, they're not ubiquitous or influential enough to 'define the decade'.
That's another thing, influence, in the waning popularity of the alternative rock of the late 90's and hideous 'punk' of the early 00's, the majority of popular rock music is chime-y U2 knockoff music, and there they are still standing head and shoulders above those competitors compositionally.
Those are the reasons why I'd actually vote for them, along with what Coriander said.