people keep arguing "aah what about PC??? i can play PC games and those wont cost me anything online!!!!"
Because a PC isn't bound to a single service, nor is it just for gaming. The reason Steam can remain a free service is because of the overwhelming number of titles they're taking 30% from. They also limit your community features (friend list size, profile content, etc) unless you play into their community market, which, also gives them a profit. And when it comes to PC, in most cases, there's either some sort of microtransaction, or the players host the servers themselves.
It wouldn't make sense to have a PC require a monthly subscription. It's an open platform spanning multiple OSes. Each console is a closed platform running on a single service and a single OS.