I was looking on xbox.com, reading through some stuff, and noticed something. At their conference, it sounded like they were kind of throwing in against the free games that come with PSN Plus, but it clearly says on their site:
"As a gesture of thanks to the millions of Xbox fans around the world for their passion and loyalty, Xbox announced that every Xbox Live Gold subscriber will receive two free Xbox 360 games per month until the release of Xbox One"
So it would seem to indicate this is not a permanent feature, but just something leading up to the new console release. I'll have to go back and watch that part of the conference, but I don't think that was made clear at the time.