I've used Ccleaner for years, all the while assuming that it cleaned up EVERYTHING in the registry, until just now. I uninstalled a program then tried re-installing it only to see that it could see numerous paths, etc of previous installs. Then, I start examining my hard drive, and registry only to find a ton of entries it left in the registry. What's the deal?
It simply gives a quicker access than Windows Control Panel to whatever un-installer was included with the initial installation.
Blame Adobe or whatever the supplier was - they are guilty of failing to do a clean job.
even things like .Net leave broken stuff behind on a clean system installation.
at least with the registry cleaner built into ccleaner you can find some of the stuff left behind.