Companies like Symantec has been doing this for many years. They charge an annual fee for virus definitions. The difference is that if you stop paying, your old virus definition is still functional. But with Adobe, your software won't work if you don't pay. One danger I see is that all the Photoshop files you have created, while you are using the software, and you can't open them if you are no longer a subscriber. This is just wrong. You are basically held hostage by Adobe. Perhaps that's what they are counting on for continuous subscription. If you want to open your files created with Photoshop, pay up!
As good as Adobe products are, I think it's time for me to consider alternative. Corel, Phase One, and many others offer RAW converters and image manipulation software. I am pretty sure more players will enter this market to fill the gap that Adobe has left open.
No software is irreplaceable. Not even Photoshop.
Untitled - Canon 10D & Pentacon 50mm f1.8. June, 2005.