It depends what you want from uni life and what kind of nights out you're into. Loads of people come to london for uni and have the best time of their lives so to say its not a student city isn't completely true. There;s plenty of places to go, house parties, student unions, one or two student nights and all sorts. Sometimes I love it, sometimes I wish I'd gone to some other place.
One thing I've got to stress is that it is not as dangerous as people make out or assume, some of the really cheap really good areas (new cross, dulwich, peckham and camberwell) get overlooked by people who are scared of getting mugged and killed or just generally a bit weary of large groups of non whites, its these areas that have the most going for them in terms of student lifestyle, espesciially new cross. I walk around by myself at like 3-5 in the morning with no qualms at all.