Ok here's my opinion, and its coming from someone who listens to Darkthrone, Burzum etc. for anyone that cares.
I like Dimmu Borgir, and I would have to agree with the melodic thrash will black metal elements statment. Going back to the original topic of this thread, I think they aren't considered "true" black metal because really they simply aren't black metal.
People are looking past the music and seeing increased production and more commercial promotion and assuming that they've sold out, thus making them "false", and thats not really how it should be seen.
I personally think the whole "true" BM idea is rediculous. If true black DID exist at one point, I think it was with Darkthrone, Burzum, Mayhem etc. in the early 90's. If I replicated their sound and used thin production today, would my band be labeled as "true"? I sure would expect it, but some people...
and yes, PEM is the shit.