There has been a lot of confusion out there in the market about Adobe's plans to move to the cloud "Creative Cloud." The 1st question that I get practically every day is "Will I have to run my Apps in the Cloud or can I just download them and install them as I do today?" The answer is that CS6 will be available as a stand alone installable App just like CS5 and CS5.5 are today. You will NOT have to use Creative Cloud or buy a subscription if you don't want to! Subscription is an alternative method to having a big cash outlay to buy Creative Suite. It's an OPTION (like leasing a car vs. buying one). Even with Subscription you're downloading the Apps and running them on your local machine and not in the cloud. The choice is yours. Now with that out of the way, here is a link to the recent policy changes that spell out upgrade paths for CS3 and CS4 users.
Yes, CS5 and CS5.5 users can upgrade too. It was never an issue for current users to go to CS6.