True, it is his money and I'm no judge as to what he should spend it on. My point still stands though that I think there are better ways for him to spend his money for his enjoyment, for other people's benefit, and for the sake of supporting Harmonix. Buying 3 versions of the same game didn't give him much added entertainment, it didn't bring a lot of support for Harmonix, and it did nothing for others who may want the game but can't afford it.
The way I interpreted it, he has all of the instruments for all of the systems. Now, that could be anywhere from $750, if he bought all limited editoins, or a couple hundred dollars. Then he bought 3 of the game, for around a couple hundred dollars. DLC for all 3 games cost yet another couple hundred. Maybe he bought another console just to play the game, yet another couple hundred. Finally, who knows if he bought those limited edition guitars, which could add another $600 to the cost.
My point still stands. I think it was entirely unnecessary and he could've enjoyed the game for just as long on one system. Plus, judging by that profile pic of his (asuuming, of course, that that is him) he looks like a kid still living with his parents.