I do think that Salmons was piqued when he got bumped from the starting lineup by Artest after averaging 20/5/5 as a starter, which was a bit delusional. He could have averaged 40 points a game and Artest was still going to be a starter. But I really don't think that Salmons is a pouty player. I think he gets an unfairly bad rap for how he plays coming off the bench, and I question the conventional wisdom around here that he has a bad attitude. He always plays hard, he was the most consistent defender on the team whether his offense was working or not, and he plays unselfishly.
The thing about Salmons that makes him ill-suited as a bench player but good as a starter is that he really picks his spots and opportunities. Like Kevin, he mostly plays within the offense, he doesn't tend to force action, and since he's not much of a spot-up shooter, he is basically dependent upon picking his spots and being opportunistic on offense. Over the course of 30 minutes as a starter, he may have 15 quiet minutes offensively followed by a 20 point burst in the next 15 minutes. As a starter, his stats are fantastic, and that playing-within-the-offense character really meshes with Kevin Martin. But if you break up those 30 minutes into two, if he were coming off the bench that's a 0 one game and a really good game the next, which is essentially the patented John Salmons coming off the bench pattern.
There are some guys who can contribute in bursts off the bench and are ideally suited to that role, there are some guys who are better starters. There may have been some pouting going on, but I honestly think the bigger factor is just that the way Salmons plays is more conducive and consistent when it's stretched over 30 minutes rather than trying to expect him to make something happen in a short burst.
Garcia, on the other hand, is one of those players who is ideally suited to a bench role because he can come in, make some things happen, bring energy, and make one or two supremely boneheaded plays.