Why do cats vomit anyway?

Why do they vomit?  This is an eternal question that I think every cat owner must ask at one time or another.  Cats vomit.  That's just how it is.  While I can certainly think of plenty of perfectly good physiologically sound medical reasons for a cat to vomit, which certainly do happen and should be taken seriously, sometimes it seems like physiology has nothing to do with it.  For instance, one of my favorites is the vomit placed strategically just inside the doorway to my bedroom in the evening.  Of course I won't see it entering the dark room, and I will be sure to step in it with my stocking feet, or worse yet, a bare foot.  Yuck.  You can't tell me the cat didn't get some strange pleasure out of that.  There's also the vomiting on any available soft fabric.  I have hardwood floors, no carpeting, and as few rugs as possible.  Yet, with vast expanses of hard, easy to clean surface, the cats will inevitably vomit just on the edge of whatever rug is handy.  They could  have moved over just two inches and avoided the rug, but no, that would be too easy.  But nothing, and I mean nothing, is as bad as the strategically placed vomit on the bed.  Preferably on top of as many layers of bedding as possible so that you need to wash everything.  Of course, you won't discover said present until actually getting into bed to cuddle in for sleep, making the event all the more fun (for the cat who is probably curled up as cute and innocent as can be on a clean blanket somewhere.)  Alas, once they're curled up next to me, purring contentedly, I always forgive them, and think of vomit duty as one of the occasional annoyances one must endure for the privilege of living with such creatures.