Several years ago I was at Worstbuy replacing my dad's mp3player, he bought the extended warranty. Anyways, while I was waiting for them to give me a replacement I went to the parts section (which is anemic in choices). I noticed that there weren't any cpu's, so I asked a rep (was actually geek squad) if I could see their cpu selection. He took me to some prebuilt machines.
[/facepalm]
I have it when people refer to the tower as a cpu. It isn't a cpu and never was. That's like calling a car an engine. I don't know where the habit came from, but engineers don't say it, so I can only imagine somewhere in the past when someone was getting their first machine they misunderstood the tech guy and started calling it a cpu. It snowballed form there.
It's right up there with calling magazines clips ,in annoyance.