I've often seen this question asked, and I don't think it's just an imaginary pattern. Here's my armchair economics-based analysis.
Real injuries in soccer are usually intensely painful, but brief (particularly shin and other lower-leg injuries--even with pads, they can still hurt). An injured player may briefly be in agony, but it ends quickly and the player can get back up.
This means that it can be difficult for a referee to tell a real injury from a fake one. If the referee is fooled, the penalty to the "offending" team is the same whether an injury is real or faked, so it pays to fake injuries. Furthermore, there's no disincentive to fake an injury--the referee is not going to penalize a team for trying to make the other team look guilty. Even if the referee wanted to do so, he'd have to use replays to reliably find the truth, and soccer fans cannot tolerate the delays that would be associated with replays. Maybe they could fine players after a game upon reviewing a recording of the game, but I suspect the fines would have to be really big to change player behavior.
So to sum up: In soccer, faking injuries is pretty much all benefit, no cost. Again, this is merely an armchair just-so story. I'd be interested in hearing other just-so stories, too!