Gaikai not a Subscription Service
While both Gaikai and OnLive promise to deliver on-demand streaming video game play without the use of an expensive console, they're going about it in two completely different ways.
OnLive is targeting consumers, and wants to sell their service directly to you for $15 per month, plus whatever rentals and purchases you make. As Gaikai co-founder David Perry recently told Joystiq, his service is taking a completely different approach:
"People do not come to us to play games, they play the games right on the publisher's site. The publisher uses our technology to make it all possible. So from wherever you click, you end up on the publisher's site with the latest version of the game."
The idea is that if you go to Ubisoft's website to check out Assassin's Creed III, for instance, you'll be able to click a link and try the game out right there on the spot. If you like it, you'll be able to buy it and just keep on playing. So Gaikai intends to sell their service to publishers, who will then turn around and provide it to their own users however they see fit.
You will never have to buy Gaikai, though you may buy games through it.
-calimer