How could you be an equal player if you don't own, at least, the player's guide to the game? If everyone else owns the rules, then they can spend equal time on the game. They might not, but that's their choice. If you have to borrow books to play, then you cannot.
I don't think owning the books necessarily translates to knowing the rules. I could get plunked into any 3.5 D&D game and be fine even if I didn't own a book. I'd probably know the rules better than half the group.
I don't require people to own the books of what we play. However, if you don't own the books, you also don't get to choose the edition of whatever game we happen to be playing.
I think he was saying he wanted his input to be equal to that of the other players, not that he wants to single-handedly choose the edition for the group.
For example, say there are five players and a GM, and the GM is well acquainted with two different editions of a game. Players A, B, and C have the books for Edition One, while player D has Edition Two, and player E player has no books (the GM has both sets of books). The players talk about what game they want to play (the GM is open to either, and leaves it to them). Three players vote for Edition Two (players C, D, and E), while two players vote for Edition One (A, B).
Do you play Edition One because you have more books? Do you play Edition Two because more people voted for it? If so, does that mean that player E is getting equal say (even though he has no books)?
I understand that as a GM, you may just decide to play Edition One in this scenario because it has more books, but if you're deciding based on player input alone, do you discount player E completely, or is he the tie-breaker (meaning you play Edition Two)?