I bought the PS3 version. You need to have access to a PS3 to activate it on your Steam account, and it ties your PSN account to your Steam account.
The disc is completely detached from the PC version, and is only needed to activate the key on your Steam account. If you don’t own a PS3 but can use a friend’s for 5 minutes, you will be set.
I got the game when the PSN was down, and played the whole thing without being connected to Steam. Once the PSN came back up, I linked it to my Steam account and it played exactly the same.