last i checked, bands write music, not record labels. maybe a band wants to make it big so they write mainstream music, maybe the labels only pick out mainstream bands, depends. killswitch engage isnt really that mainstream, and i would hear them on the radio plenty of times (how i found out about them), even though it was their calmest song. to me it seems not as much the labels weakening music as much as public taste. the general public likes music thats easy to listen to and that is catchy, always have.
over the past year ive wrote a lot of different types of music, from idustrial to happy hardcore to death metal, but the one i was writing for a while was more alt metal, stuff on the radio, because thats just what i felt like writing.
theres always internet radio stations (itunes has a decent list). want to listen to more intelligent metal, try snakenet. they usually play what the radio stations dont. lot of music ideas on them without having to actually pirate a song.
as for me, yes and no. i have because im very poor and was studying other genres, also replacing CDs ive lost over the years. but im not the type to just download thousands of songs a year. i usually end up deleting all my songs every few months anyway. a lot of bands put their main songs up for download or at least to listen to on their website, especially mainstream, as well as music videos. the industry knows how powerful mp3 is and they are trying to use it creatively, instead of conntinue to fight it.
from an artist standpoint, its just more publicity, which = more shows. you may lose like 10 cents off of that sale, but gain a few bucks from the shows you do in their area.