Yeah I was going to say the same thing... that's a photoshopped image. Perkins hasn't suited up since game 6 of the Finals, yet he is in that picture.
The way I see it, there is a difference between conditioning and body weight. Paul Pierce has never been toned, and during at least one or two seasons from his past, noticeably overweight. That '06-'07 year when he was plagued with injuries was his worst in terms of shape IMO. In an interview that year, he said he had gotten up near 250! But Pierce has remained a very healthy player over the course of his career. He usually plays in just about every game every season.
Jermaine and Shaq on the other hand have had injury problems, especially over the latter parts of their careers. Conditioning is a constant process and when one is not equipped to retain ideal shape, they gain weight. And when they get back on the court to play, they're not at an ideal weight / conditioning level to play at their optimum level, which puts them at risk for even more injuries down the road. It's a deadly cycle, and one I think both these guys are a victim of.
Earlier in the thread, someone posted pictures of Jermaine over the last few years in his career. Personally, while I think pictures help give an indication of body weight / size, they don't show his entire body. You have a better glimpse of a person's shape by watching them on TV.