Why is Andy Schleck at the Dauphine if he's not even going to keep up with the peloton? If the idea is simply conditioning and getting more race days in his legs, one would think he'd at least want to keep up with the main bunch.
As for only racing to win in the TdF, Schlecklet takes that approach to extremes. If his wikipedia entry is correct, his only major victory in other races was the 2009 Liège–Bastogne–Liège. That's it. All that talent. One race.
I'm reminded of another TdF rider who was much maligned for focusing solely on the Tour, Lance Armstrong. He won a world championship (granted that was long before his TdF wins), La Flèche Wallonne, the Tour of Luxembourg, the Tour de Suisse, and the Critérium du Dauphiné (twice). It's not much for a 7 time TdF winner, but at least he occasionally raced to win outside of the TdF.
Wiggins and Evans are certainly preparing for Le Tour, but they're also putting in strong performances at Dauphine.