WW, I think the Pixies and the Pumpkins borrowed a few tricks from metal but I certainly would not locate them within the genre. It might be worth noting that I think a lot of bands that have been mentioned in this thread (GnR, AC/DC, Evanescence) are not metal, even if they were influenced by it.
In reply to:
Ville: The essence of True Metal can and will be debated until the end of the world.
What is and isn't "true metal" (and that is what they call it) is notoriously divisive topic among metal fans. Part of the problem is that metal has changed so much in it's 40-odd year history. If Black Sabbath was formed today sounding exactly like they did in the early 70s, most folks would hesitate to call their music "metal." To say that something is not "true" is to say that it's not in line with the current stylistic movements of the genre. GnR might have been true metal if they'd released Appetite for Destruction in 1971 instead of within a year of Scum, Reign in Blood, Sign of the Black Mark and Gluey Porch Treatments. By that point, metal was about more than just the monster riffs and stoned solos; it had begun experimenting with speed, technique, atmospherics and brutality in a way that Axl and Slash did not.
I guess what it comes down to is whether you want to consider anything that uses conventions borne of metal a metal band, or only award that title to groups who occupy or have occupied a legitimate place within an aspect of a stylistic movement within metal as it was happening. There are plenty of people who are still stuck on playing jazz as it sounded in the 1940s. Does that make them not jazz musicians? I don't know. But I do know that it makes them suck.
If you hate melodic metalcore like I do, then you might find this amusing.
You know who else makes creatures? Satan.