They have this weird drafting system tho, so I guess it's not the same team after a few years. Well, I don't know how big a fraction of the team changes teams after a season.
It differes based on the sport. The NFL is the most "equal" between teams. It's nice because you don't have the same teams winning year after year. The worst teams get the best picks in the next draft, so theoretically they should get a boost (although some teams still manage to screw it up). In baseball, and to a lesser extent basketball, the "big market" cities tend to dominate the sport. Which sucks when you're rooting for a small market team that is always getting destroyed by the NY Yankees or the LA Dodgers.