I ran a Mutants and Masterminds game for 10 months. I had four player's buy the Mutants and Masterminds rulebook. I had two player's pick up Ultimate Power supplement. I myself purchased the rulebook, the pocket version of the rulebook, the gamemaster's screen, Ultimate Power, the M&M Gamemaster's guide, and several adventures.
No one bought a PHB, a DMG, or MM. No Races of... or Complete... were purchased. WoTC did not make a dime out of my game.
And yet I had character sheets that had Str, Dex, Con, Int, Wis, Cha. I had feats, I had skill ranks, I have Fort, Ref, and Will. There were DC's and an 18 Strenght meant a +4. And, of course, we rolled a d20. Sure there were changes to the game (really GOOD changes btw), but this was clearly a game based off of dungeons and dragons d20 mechanic. And yet WoTC derived (and would derive) zero cash flow from it. I had several player's who never even played D&D (and still haven't).