I've determined that i despise the term sellout when it comes to musicians. I pretty much entirely agree with Frosties on this issue, but i'll comment on the whole In Flames thing. I made a thread talking about bands like In Flames and Soilwork, whose early music was great to me, but both bands then got much more commercial sounding and, to me, made shittier music. But the thing is, that doesn't mean those bands "sold out." It just means they felt like making different music that now doesn't appeal to me. The moment you are getting paid for music is the moment you "sell out," so pretty much every band you know has sold out.
The Dresden Dolls guitar player actually gave a great speech about the whole selling out ordeal at my school (Northeastern University). He pretty much said what i just said, that people like to say bands they used to like sold out once they start making music they no longer like/music that is more popular. If an artist wants to make something that would have more commercial appeal, why shouldnt they be able to? It's their music and they can do whatever they want with it... they shouldn't have to put up with a bunch of stupid fans that instead of just finding another band to like, will complain about how their favorite band sold out. If you dont like a band anymore because they changed their sound for whatever reason, find new bands.. don't whine about it.