It still come back that after three years, sure you have a copy of cs6 but none of the PSDs you've made using CC will work fully. Then they jack up the price at the end of those three years and now your hands are tied. Do I trust adobe to support CS6 with updates? Nope. They've never done it in the past with any releases. They simply released a new version of PS. Yeah, now you are just creating conspiracies from thin air. My files from CS2 and CS3 still work in CS6, and seeing as Creative Cloud is based very much on CS6 w/ upgrades, your PSD files will still work. Or, you can save them as .tiff, .dng, or a variety of other formats that work perfectly fine in a dozen other programs.
You have it the wrong way around. It's not the question if your CS6 files are going to work in CC but if your CC files will work in CS6. (As this will be the last version you'll be able to use if you stop using CC) And that is going to be a big if. That is putting a lot of trust into Adobe and their shareholders. If they at some point decide to change the PSD format so it wont be compatible with non CC versions you'll be stuck dead in the water. Since the updates will pretty much roll out without you knowing about it they can all of a sudden switch off compatibility and by the time you realize what happened a big chuck of your work may already have been saved in the new format.
I am not again CC, but I am against having CC as the only option. Because this clearly points out that Adobe wants to pressure people into the CC model. They do not want to give people a choice. And a company who does that might just decide to up the pressure a bit more down the line. TIFF and DNG are all fine as long as you don't rely on the ability to change effects or layers later on. Personally I often use that ability with my images and loosing the actual PSD with all it's functions would mean I would have to start from scratch.