Ah, I've experienced this recently. A friend of mine got me into Flight of the Conchords, quite a while ago, and for a brief time we discussed them alot..sent each other videos, etc. That died down after a while (although I continued to like them), and just recently I was wearing a Flight of the Conchords t-shirt. When he saw it, he made a derisive noise, so I asked him why, and he said "I hate them now...they've got all popular..and sold out and stuff.." and then tailed off. Lost for words, I simply gave him a slap around the head.
I hate this concept of "selling out". The purpose of the band is to make money. Call me cynical, but I would bet that almost all musical groups ARE concerned about the money they make, regardless of what they say about it just being about the music. Thus, we should not be surprised, or disappointed, when they do things that make them more money. Sure, be disappointed if you don't like their music anymore, but not because they made a high-budget music video, or got more 'mainstream' or something.