Evans got into the maillot jaune by virtue of doing decently on the cobbles and not being dropped by more than 10 seconds on Morzine, a climb where pretty much no major contender save for Armstrong and Wiggins lost more than ten seconds. No way was Evans, after one of the toughest GTs in years, and after the great Ardennes campaign he had, holding on to Andy and Alberto on Madeleine. Sánchez left the others there too. Evans ran out of steam in the Giro, and he would have had even less left in the tank at the Tour. He's a much smarter rider now than he used to be, but his best double-GT showing is 2nd in the Tour, 4th in the Vuelta (in 2007) - and that in a pretty light Vuelta route. And of course, the Tour péloton is much faster than the Vuelta péloton, which is one of the main reasons the Tour-Vuelta double is perceived as much more doable than the Giro-Tour one.
Evans would have been 5th at absolute best in the 2010 Tour. Remember the guy that beat him in that horrendously difficult Giro? The guy that hadn't had to do it off the back of a tough Ardennes campaign? The guy that didn't have an injury? He finished 32nd at the Tour. Sastre, by contrast, had a difficult time of the Giro and finished 8th. But he'd had next to no other racing, and still could only manage 20th at the Tour.
Evans is good. He's really good. Sometimes even phenomenal. But he's not bionic. And that's before we consider that the 2010 BMC support team, well, half of it wasn't ready for ONE Grand Tour, let alone two. I place the 2010 Evans in the lower half of the top 10 at the Tour at best. Not because I don't rate him, but because I think people who think he'd have been in the top 5 or contending for the win really undersell how hard he'd had to work in his 41 race days to that point. Basso had roughly the same amount of race days, but had basically hidden in the péloton until we got to Trentino. Evans had been fighting for the win Down Under, at Tirreno-Adriatico, at the Critérium International and the Ardennes before we got to the Giro. His team needed him to. There's only so much recovery a man can have.
What about Vino? I hear you ask. He was 6th at the Giro and managed 16th at the Tour whilst being a super-domestique! Yes, but despite his successful season, he really hadn't shown his face in much until Trentino; he did hold his form impressively, admittedly, from LBL and through the Giro, but like Evans he faded from contention in the final week at the Giro, and he wasn't exactly trying to win the Tour; the pressure was off so he didn't need to worry about fighting to be in the front groups on flat stages, and could let himself drop time in the mountains (especially as he wanted the stage win, so dropping time was actually beneficial to this goal). Vino was successful at the Tour precisely because he didn't have that weight of expectation. And he still only managed 16th.