I like some rock music but I'm no connoisseur. Dahl hit the nail on the head - most rock fans I've met think that:
techno = nosebleed acid 303 type sounds and fast hard beats (I've been to some funky techno nights which are the antithesis of this - relatively laid back, funky basslines, and a great chilled vibe)
trance = cheesy vocal / big riff stuff (what about progressive trance, the more melodic end of prog house, subtler breakbeaty stuff like Hybrid, etc.)
drum+bass is either 'okay' (i.e. they haven't really heard any but they know it's got some credibility) or 'crap'
people who like 'dance' music = people who only listen to chart music
...and are pretty much unaware of any other styles of dance music. Likewise, I think a lot of peoples' perceptions of rock music are coloured by Limp Bizkit, Marilyn Manson etc. It's the same with any scene. Snoop Dogg and Jay-Z don't do hip hop any favours either
The only problem I have about the rock scene is attitude - I've seen quite a bit of it. It just seems to be a bit more negative, a bit more aggressive, and a bit more dismissive of other styles of music. And there's too much dissing. Just the other day I saw this teenaged girl wearing a Nirvana t-shirt, and I overheard some prat scowling that 'she was still sucking on her mother's tit when Nirvana were big'. The guy was clearly disgusted - he evidently thought that 'true' Nirvana fans (like himself, probably in his mid-twenties) were the only ones who were allowed to like Nirvana. Talk about making a big deal over nothing... But I've heard a lot of this kind of thing. And all that pretentiousness about 'oh, I liked their first album but then they got too commercial...'