I don’t know how anyone looks at 2011, and concludes that Bert has much chance of winning the TDF following the Giro this year. He was probably at his peak that year, and though the Giro had a tough course, he dominated it, which means he didn’t have to go all out in the later stages. And still he didn’t really challenge for the yellow in the TDF. A Tour in which so many big names crashed out early—Wiggins, Vino, Klodi, Horner, VDB—that one could describe the last two weeks as one with a relatively weak field.
To be fair, Bert also crashed twice in the early stages in that Tour. As a result, he lost time, and possibly form, how much we can never know. Had he not crashed and lost that time and perhaps strength, he might have podiumed, but again, in a field decimated of other contenders. I don’t think that even absent those crashes he would have been a serious contender for yellow.
I think he’s in the Giro because he wants to join Hinault as the only riders to win at least two of each GT. I think he sees the Giro as pretty much a sure thing, whereas if he focuses solely on the Tour, and doesn’t win, his season will be a huge disappointment. I’m sure he’s telling himself that he can win both, but you could say a strong streak of denial is an important part of every major athlete’s toolbox.
Bottom line: how is this year different from 2011? Is he stronger now than he was then? Highly doubtful. Is the TDF field this year weaker than it was then? No way, particularly if you compare the start list to 2011’s finish list (remember, Tommy V. almost podiumed).
And same with Froome, who also has tried the Tour-Vuelta double before. This one at least makes more sense, because if you win the TDF, you don’t care that much if you don’t win the Vuelta. But the odds of his doing it are IMO really small.
Which suggests an answer to Rhubroma's complaint. Suppose the TDF was the first GT of the season, instead of the second, and followed by the Giro. Then we would see a lot of riders going for the double, because after winning the Tour, the Giro would be just frosting on the cake, rather than the biggest race of the season. I assume this is very unlikely to happen, the TDF would have to be held earlier, but if organizers wanted to encourage riders to do both in the same season, this would be the way to go about it. Maybe if several major contenders got together and expressed their wish to do the double, the format could be changed just for that season, and occasionally in others?