Harmonix and the console providers already collect enough demographic, sales and preference information about us that, combined with say a comparison using Pandora's Music Genome Project engine of previously purchased DLC vs available non-ported RBN tracks, they could project future PS3/Wii RBN sales reasonably well. The null hypothesis would be that, among common tracks, XBOX and PS3/Wii RBN existing sales are proportionally identical, and deviation from this would give more weight to the demo/pandora analysis.
This works best at the micro level because the projections would be for individual RBN tracks. Unfortunately, tracks packaged together in each game release have no DLC sales track record from which to project. (For example, there's no individual sales for Cure, Def Leppard, INXS or Tears For Fears tracks yet.) They can, however, use replay counts as a sales proxy because they collect all our play stats, enough to make an informed decision to release, say, "How Soon Is Now?" (Answer: $$$$$$$$$$$)
Now HMX has limited artistic input for which independent developers are creating specific tracks, but once submitted completed tracks would be subject to this analysis. Example: YNRNRF by Sleater-Kinney is their only DLC track, and based on the leaderboards was not a giant seller. Their three tracks in RBN (Jumpers, Entertain & Rollercoaster) have yet to be ported, and I would argue the demographic/pandora sales comparisons would be classic rock consumers (esp for the instrument parts). I might request these tracks in the RBN port thread, but that's only one vote (and some others) among people predisposed to read the forums and actually post something. Expressing my opinion in this manner does not outweigh a reasoned argument about whether these tracks would sell well enough among the gaming population. I want that argument to be based on more than top XBOX sales, though.
How do we know XBOX and PS3/Wii users are different? If we were the same, we would have bought an XBOX.
Crap it's late, if this makes any sense please take it seriously...
Well I do like the current state of the PS3 RBN (for the most part - 5 song limit and a few others things could definitely be improved). It's not like regular DLC provides enough content for the average metal fan, so this feels like a great way to even things out. Still waiting on Sybreed, Emperor, Van Frisia and a few others though.
The PSN song limit / genre restriction is small potatoes next to the fact that 90% of the songs we got don't have proper pro charts (cymbals only), which pretty much ruins them for me.
Metal songs sell on the 360 RBN. Therefore, HMX sees this and releases this for the PS3/Wii because they believe it will sell well on the PS3/Wii (and they're right).
Moar Grateful Dead:
Led Zeppelin (I can dream, can't I?):
honestly there are so many better metal songs than what were getting on ps3, and more prog and punk would be lovely
I think it's time i join those who put mostly unfulfilled requests in there signature; ROCK BAND NEEDS MORE COCAINE
I stopped reading when the OP turned it into a "What is actually ROCK" debate.
Tiger Uppercut: Platinum Artist | Expert: G/B | Hard: D/V
Song Count: 831 | Newest: "Great Balls of Fire" & "Dog Days Are Over"
Whats this?! Variety?! Only 1 metal song?! and its one thats been requested?! OH MY GOD THEY'RE ACTUALLY TRYING TO CHANGE!!!! Happy Day!!!
1298 songs total - PS3 - PSN Bobman32x
Bands I'd love to see as DLC for Rock Band:
Bal Sagoth 
The only problem with RBN on the PS3 is that it doesn't have enough novelty and amberian dawn songs.
No, I'm not being sarcastic. I want Felicia Day and the rest of Amberian Dawn. I am squarely in the demographic that buys novelty songs and (melodic) death metal. I also buy the grunty death metal songs sometimes because they're actually pretty fun to sing on vocals.
I AM PART OF THE PROBLEM AND I'M LOVING IT