Ah, ok, now this thread makes a lot more sense after this post.
I think it probably has a little less to do with talent/creativity than it does with risk-taking. The two 45% groups have very well-defined genre-names that can be applied to them. The whole framework and fanbase is already there. In contrast, if you're in the 10% group, a record label says, "uh, sorry, we think you're great, but we'd have no idea how to promote you!" It's much safer to do something that you can easily sell to brain-dead fans with a "Sounds Like..." sticker stuck to the CD.
Of course, the existence of pre-fab genres makes it easier for completely uncreative bands to get attention too, but I'm sure there are lots of quite-creative people out there playing to a genre just because they have bills to pay.
Sometimes I think that the "doom" genre is lucky to have escaped this 10%. Maybe it's because I'm not a doom-freak, but I feel like the number of "doom" bands is relatively small compared to other genres. But at some point the number of bands playing that kind of music reached a critical mass, coalesced into the genre someone cleverly labeled "doom", and then continued to attract more bands, because, "hey, now there's this new 'doom' genre! It's safe for use to do that..." So it's almost like there's a precedent for bands that want to lift themselves out of the dreaded 10% without compromising their ideals: they just need to find a good coalition of similar bands and come up with a clever name.
Anyway, now that someone finally mentioned Orphaned Land, the only big one I have left is Root! Oh, did anyone hit Solefald yet? And Green Carnation? Ok, I'll stop, there's probably a ton more! (like you, a lot of my favorite bands come from this 10%)
It's interesting to note that there are very few real "singers" in the bands that have been mentioned so far. Meaning people that wouldn't get laughed out of an American Idol audition. And that probably points to the fact that there are very few good singers out there in general, which is why so many bands just go straight for the growls.
Speaking of American Idol, actually all mainstream/major-label metal bands fit in that 10% (Disturbed, Coheed & Cambria, etc.)
Neil