I’m not saying it’s a bad feature. I’m just saying that I know they do have measures in place to prevent gaming of the system. I don’t think the problem is as big as it used to be when they had leaderboards and whatnot. Now the main concern would be people who wanted to be listed as a number one fan of a certain group. It’s not that it’s the end of the world or anything, it’s just annoying for people to do that.
And yes, it would be possible to game the system even without playcount importing available. However, it becomes much easier when playcounts are imported. In the space of about four seconds, I could use an AppleScript (one that I already have) to say that I had listened to every song in my library 100,000 times. I could then create a new Lsat.fm account that started with almost 500,000,000 listens. Granted, the information would be useless to me—but it would still mess up Last.fm’s charts quite a bit. (Maybe they have a cap, but where?)
All I really do is look at my stats and my friends stats, so what I’m saying isn’t coming from any particular personal concern.
Side note: Plays under 30 seconds aren’t scrobbled (at least, not after an account is created).