It really depends on the genre, and fine details into the setting, period, etc. If I'm playing a game where I'm fighting modern-day terrorist insurgents, for instance, I'm going to see a lot of AK-47s, because they're cheap, fairly reliable, and they're freakin everywhere and extremely easy to get ahold of en masse, especially if you're trading illegally.
Something like that may be common, but if it's setting-correct, I don't think it's really being "overused". I think it would be rather silly if Modern Warfare 2 equipped all the terrorists with laser guns, simply because someone decided the AK-47 was "old news".
What I'm saying is the setting and genre matter a lot.