When Roger is on the verge of losing the match it usually means he was not playing as well as he is capable of, and if he comes back from a small deficit he probably was able to bring out his best tennis, which he had not been producing up until that point in the match in most cases in order to be on the verge of losing, when he needed it most.
Also a choke would have to be a match his opponent was in much more of a position to win then him. There are hardly any matches I can think of where that was the case. Maybe his 2 wins over Rochus, that is it. Roddick was never in more position to win the U.S Open final then Federer was, the year-end Championships round robin he had a match point but was never up more then a point or two in the 2nd set, none of his matches in Australia were his opponents ever in a clear winning position, Nadal was never ahead in the Wimbledon final at any point, Blake never was anywhere near a winning position in any of his matches with Federer, the closest was in position to win the first set of the Pacific Life final, big deal in a best 3-of-5 final. Except for the Rochus match his opponents were never close to being in a winning position, in any of hte matches, in any of his 3 setters in Canada or Halle. So those "chokes" are simply inventions in ones mind I suspect.
One could say Federer gives his opponents chances by missed opportunites to, should we say 2 of Nadal's wins over Federer were because Federer choked, in Dubai and Rome? Those were better examples of chokes then any of Roger's wins this year I can recall, except the 2 Rochus wins. Or somebody like Tommy Haas was only in the Australian Open match since Federer let up a bit in the 3rd set and let it get that close by laying off, one should probably say Federer "choked" to even have Haas in a 5th set in the first place. Blake was lucky to be in their U.S Open quarterfinal as much as he was, Federer served for the first set and choked, had a chance to close out the 3rd set in the tiebreak and got tight, then choked two different times serving for the 4th but closed out the 2nd time anyway, it was Blake who was in that match at all because Federer was choking, not vice versa. Lots of other examples I could come up with.