Don't forget he didn't ride for GC in either the Giro or Tour; not that that still isn't an incredible amount of hard riding but it should make a difference. He's a robust guy, recovers very well, and so far it seems like all the racing has suited him very well because he is flying. That said, there is a long way to go and the third week is still very hard. A big factor is frankly, as I said in Sepp's thread, it would be hard to imagine being in the leaders jersey at the end of the second week in a better position than he is. Pretty nice time buffer, two teammates either there to work for him or pick up the slack if he has a bad day. And if he DOES have the bad day, who except the usual suspects on here who irrationally hate the guy are going to blame him? He's got 2 2/3rds GC's in his legs; it wouldn't be a huge shock if he fades. He's got nothing to lose and everything to gain.
For me, he looks GREAT right now, happy, relaxed, and strong, and Ayuso was just quoted as saying he thinks Sepp is the strongest TJV guy. I believe he's going to do it.