Being in art school doesn't mean you're going to be a good artist, graff or otherwise. It doesn't mean you won't be either, though. Skill really comes on an individual basis.
One thing that art school can do for you though, is to teach you tons of things about drawing, painting, and colors which are all very applicable to graff, and could make you a hell of a lot better.
Plus there's shitloads of art school students who don't have rich parents paying their tuition. They do work study, or take out loans which they have to spend the next 6 or 8 years of their life paying off.
Not taking a side here, just saying: Don't diss a writer just because he goes to art school. There are plenty of cocky little art bitches just riding the trend, but there are some genuine talents who put in tons of work as well. Nothing is just black and white like that.
Anyway, thats my two cents.