I'm not trying to be rude or anything...but I often 'blitz' my friends list to get rid of people I don't talk to anymore. I hate it when people say "yeah you have 400 friends but you don't actually know any of them".
There's a big group of people I went to junior school with on my facebook, they all added me, it seemed rude to say no, and sometimes it's interesting to find out what they're doing these days. But a few months later and about to go to uni...it seems a bit stupid considering I was never really friends with them in real life anyway, yet they're popping up on my news feed all the time.
There are also loads of random 'internet' people on there who I've added at some point from forums etc, but we don't talk anymore and half the time I forget who they are...I don't want their birthdays coming up in my events and all the rest and I know we don't have any reason to speak anymore.
I think that's the reason it didn't happen on myspace- at least when I used it, there wasn't a news feed, there were just bulletins which were easier to ignore. Plus adding someone was more of a considering decision because you actually had to go on their page.
People from my high school have deleted me now we've left though, which I thought was a bit rude especially since I considered some of them to be friends. Sometimes I delete people from high school myself though...because knowing that the 'popular' ones from school can read my statuses makes me tailor them or sometimes not post them at all...it's nicer to just have your friends on there and be able to say what you want without people being sarcastic about it or whatever.