I've had a similar experience in an indepentant computer store. A friend of mine and I went in to the store to check it out, and ended up talking to the guy who owned the place, a bearded red-faced man in his 60s. We then happened to mention the faultering Hauppage TV card that was recently installed in my friends computer.
The guy then literally took off! "Is it an AMD machine? It's AMD isn't it? That's why it isn't working!" admitedly it was and AMD machine, but considering the problems it was extremely unlikely to be the root cause; it was just a duff card. But the foroscity the guy took on as soon as we dared to say that AMD wasn't the problem, we felt compelled to leave the shop very quickly. I think my friend's parting words were "I'll bring in the stats to prove AMD is better." although we never did return.
I've never understood the fanatisism over processors, to me it's entirely down to whatever will do the job best, for the cheapest price.