I can see both sides of this argument. And while I wouldn't say that "everyone's doing it", I lump buying likes in with other types of SEO. Well, okay, it's like a slightly more deceptive version of other types of SEO.
The thing is, yeah, if you have more "likes" on FB you have more visibility. BUT, all likes are not created equal! A random "like" from some fake account in Grenada where nobody will ever hear your music does MUCH LESS to increase your visibility than a "like" from someone who has friends that will dig your music, or who has friends who have already liked your page, etc.
So your time and money is better invested in building a REAL, LASTING web presence than the "quick fix" that fake Facebook likes provide. Trust me on this one - I get paid to do this kind of thing every day.
EDIT: My band doesn't buy likes. I guess I would compare it to adding your website to an "autosurfing" ring so it seems more popular than it is. Well, my band doesn't do that either. Our web presence works well for us because I created a tailored solution that effectively communicates with our fan base. I can't see us needing to buy likes in the future. I'm too good at the Internet for that.