Of course, avoiding prestige classes means you don't have to use your skills and feats for things you wouldn't normally want. I have an 18th level sorcerrer and he would never think of entering a prestige class, simply because he has chosen the skills and feats he wanted, ratherthan the ones which let him into a prestige class.
Of course, I don't allow the broken Mage of the Arcane Order into my campaign, nor is it set in Forgotten Realms, which means no Incantrix's, Archmages, etc.
He may enter an epic prestige class if one comes out that looks enjoyable.