Wylde and Pantera are not the first people I think about when it comes to metal, but I agree: Dickinson or Halford are turncoats, even though I have to say that at least Dickinson switched back to metal with "Accident..." when it still was not the most fashionable thing.
My naming Grohl an outsider means that he is not involved at all in what we call the metal scene and has never been because Probot was the first time he ever played metal. His hardcore background is actually more promient in the album, the components that go along with what is accepted by metalheads are more or less the general consensus: Motörhead, Venom and maybe King Diamond. Trouble is a surprise as well as Voivod. The majority of the participants share this hardcore background as well.
It does not matter where you are coming from when you play metal - it is the reasons for which you do it. The same goes for writers: I write a lot for a progressive- and fusion-zine, even though I was socialized by metal, which is my primary focus still - but I can write about these genres, because I love them as well and claim to understand what they are about.
I see that Dave goes a little too far when he shoots at Grohl several times for things he said in the past. Also, it is not that Probot hit big and kickstarted a trend. Maybe it has taken the fear off some indie people to overtly utter their fondness of metal, but anyway...
...but The Flaming Lips covering a metal song does not mean they are a band from another genre that plays metal, does it? - It´is more a matter of paying tribute to an influence of theirs, I think (if it has been done seriously). I believe that Grohl did this thing for the right reasons, be they nostalgia or digging up his roots. He does not need the money from such a project at all, needless to say.
But to come back to your initial statement: if we only let the music do the talking, what will be the use of forums like this, magazines and the wiseass-writers and -fans we are?