It is! And not only for exclusives... In fact, if I liked a 360 game a lot, I often ask a friend for its PS3 version just to have an excuse to play it all over again until I get the platinum.
When MGS2 and MGS3 HD were about to be launched, I decided to play MGS1 so I could say I have played all of them. So I downloaded it for the PC, since I didn't have a PS3 back then. Boy, the keyboard make the game a pain in the neck. I thought my space bar was about to jump off the keyboard during that goddamn sequence. XD