It's also their forum so they can do with it what they want. Most companies don't even have a user forum so how do you deal with that?
Actually, a fair number of manufacturers do have support forums, and some even have actively supported hacking. Just mention the word "jailbreaking" on the Apple forum, and the post will likely be deleted.
Also, if a post is too negative about an Apple product, it stands a good chance of being sent down the 1984 "memory hole". Of course, if it's negative towards Apple competition, it's allowed to stay. Hypocrisy at its finest.
-- When members revolted:
Back when the iPhone first came out, the forum wasn't too bad. Apple needed supporters and let a lot of comments ride.
Then came the first iPhone massive price cut and oh boy did their forums light up with early buyers complaining about being ripped off.
It was quite an amazing revolt. Former fans turned on Apple like rabid animals.
I think someone counted thousands of angry iPhone owner posts being deleted before the Apple forum moderators finally realized they couldn't win and had better let people rant. So they backed off.
The result of all that anger was Jobs announcing store credits for all the early buyers.