OEM copies of CS5.5 and CS6 are still available if you look hard enough, roughly $300 last I checked.
Interestingly, when I upgraded to 5.5 I asked Adobe directly about these and they said they are legitimate copies, but do not qualify you for upgrades. I paid $1300 to upgrade, but CC was right around the corner and Adobe knew this. I could have saved $1000 and just bought an OEM copy.
Not that much has changed to justify "not owning" it, and Adobe knows this, hence the new model. Hell, I could rollback to Word97 and miss nothing in what I use Word for. Many software programs are in this same boat now since they have crossed over into "maturity."
An ironic part with graphics is that the need to alter something "right now" comes up often, and is one tool not readily available in Windows. I have a 20+ year-old version of Paint Shop Pro 5 that installs to a directory, small (28MB-ish), and can be carried on a thumb drive. For business presentations, this has saved many people's bacon as I can edit in a couple minutes graphics on
any machine I am sitting at (no installation required). The "OMG, how did you do that?"s are rather priceless.