I'm not convinced that dead lifting is necessary for bodybuilding.
However, I can't imagine not being able to do something at a gym. Seems... stupid.
EDIT: From a business standpoint I know WHY they do it, just think it loses them a portion of the market that is necessary. If you lose all the guys that deadlift, that squat heavy, that use dumb bells over 100lbs, etc, then you lose the big and strong guys, hands down. Without those guys then I think you lose the teen/skinny wannabes. I mean, if you were a little guy looking to get big, would you be sold on a gym with no big guys in it? Even if you didn't know crap about training and were willing to give up the idea that you could deadlift, wouldn't it strike you as odd that NOBODY in the entire club weighed over 160lbs unless they were obese? If I was a gym owner I would do my best to ensure that power lifters/bodybuilders/strongmen were welcomed at all times, that they had their own area to work out in so they could be loud, slam some weights around, etc. Think of it as the "ski resort" theory. You have to have a bunny hill for those people that aren't interested in the black diamond slopes, but you have to have those big slopes visible and accessible when people are ready to move on.
Not to mention, it has been my experience that most TRUE powerlifters/strongmen/BBers are pretty polite. That is to say that your average pimply gym roid user is NOT any of the above though he may fancy himself as such.