Required attendance for raids sucks, and many guilds who have used that policy have fallen apart (like NL). Even if they handed me an engraved, diamond-encrusted invitation made of gold, and they were killing things in the Sunwell, I would not join a raid guild that had attendance requirements. The requirements in raids guilds TEND to: a) create resentment when you lose your spot because of some family tragedy that you can't help and b) attract far too many tools who have no lives and live in mommy's basement. Keep in mind that the current Number 1 raid guild on our server (BotB) does NOT have any attendance requirements (heck, they don't even have guild meetings!), they have no trouble at all with consistency in their attendance, even when they are hitting something for the 128390th time and most of them have the loot they wanted. That was one of the things I loved about that guild, and why it was hard for me to leave to come here, even though I wasn't raiding with them.
While I think it's a bit extreme to apply to a once-per-month RP event to the high attendance requirements of some raid guilds, I do think that being able to have a choice, and being around people who WANT to be there with you is much more fun than having to be around grumpy-bears who are being FORCED to be there.
-Kadi
Edit: Sorry for the Double Post, but I didn't see Toldar's response until after the previous one was written.