Hold on, we're discussing whether he's a wheelsucker, not whether he looks like a bum when he tries to ride solo. Stefano Pirazzi and Amets Txurruka can't ride on the flat and can't time trial to save their life, but are they wheelsuckers? The only people who don't spent 99,999999% of their annual kilometres in the bunch or in somebody's wheel are the likes of Cancellara who are towing other people to the finish line because nobody will let them suck their wheels, or the kind of people for whom the long range attack is their only stylistic choice for victory. Purito has reached the point where he's too dangerous to allow to attack early (and routes like the 2012 Vuelta, where he was leading most of the race and the route meant no gaps were possible until the last few kilometres on most stages since no domestiques had been adequately tired out before the final climb so everybody still had a bunch of helpers, don't help either), so his best option is to wait until they're inside his uphill-sprint range.
Cav is a truly gifted rider, and calling him a wheelsucker is kind of ignorant too (although it's still not wrong to be disappointed in the amount of races that enable him to win in the not-doing-any-work method, especially when those are races that theoretically decide who the best cyclist in the world is).
But Purito so totally is not a 500m to 3k wheelsucker. Yes, that's how his greatest triumphs were made, but because of that people seem to forget the times when it didn't work.
Take the aforementioned Val di Fassa stage. I refer you to the case of CyclingNews Live Timing vs. Giro d'Italia 2011 Stage 15.