OK... lets start with the obvious... they aren't cheap. But if you have high quality clothes... they are the only place in town to take them. I have over 20 dress shirts, each over $250 and there's no way I'd take them to a discount cleaners.
They also do a great job getting stains out. If I'm going to spend $2500 on a suit, I've got no problem spending a little more to make sure it gets cleaned properly.