I don't know about Tsonga, but Djokovic took 3 years to win another major. Who knows how much pressure he would have felt going into 2011 without a slam, DC and diet be damned?
Same with Tsonga, people are writing him off too easily. Since that final he has been in the second week of a slam 9 times, including 3 semi finals. With the confidence of a slam under his belt, he may have at least advanced to a couple more finals.
However Jo missed FO and Wimby 2008 so maybe he would have regressed anyways.