Disregarding Schleck specifically, if I was in his position, and was clean, I wouldn't feel like I'd won the Tour.
No riding down the Champs in Yellow, no champagne for the cameras, no standing on the top of the podium, no handing out jerseys to the mechanics etc, etc. Instead, he learns he's won the Tour several months later via a text message. Sure his name will be in the record books, but does Pereiro get any credit? It's utterly underwhelming.
To a sportsman, it's all about the battle, the winning on the day and the glory. That's their mentality. So from that point of view his quote*, I can fully understand and think it says nothing about whether he's doping or not.
* "I do not want to win in the offices, I want to win coming to Paris with the yellow jersey on my shoulders," he said. "I do not know what will happen, but I'm second."