I'd say this is a bold claim w/o non-anecdotal evidence. Customer service should be non-discriminatory, no matter what product/service you're selling. If I, as a customer, cannot rely on an associate to address my problem simply because I do not dress like their image, then this is not a business worth walking into in the first place.
I can walk into a grocery store with either a million-dollar suite, or a tshirt/shorts, and I still expect the same customer service.
Edit:
A simple anecdotal counter: I do not own any apple products, but I have walked into Apple Stores with friends who own Apple products. None of us dress 'the part' like your 'typical Apple user' does, but I have seen prompt customer service nonetheless.