I've never understood why orphaned registry entries were a problem.
That is a very valid point Jim. Most of the time it makes no difference a far as I can tell. At least as long as hard drives get faster and CPUs more powerful. Years back I did see performance issues when my Registry was cluttered with junk. The issue spawned a whole industry and category of applications, whether they did any good or more harm than good.
I am in the Registry pretty often, because I run a bunch of applications that break sometimes, and can only be fixed in the Registry. Or at least understood. Windows being one of them sometimes! I never reinstall Windows to fix problems (I understand you don't either), I fix the cause. But many people do just reinstall Windows at the drop of a hat to fix quite minor issues which can often be fixed with a minor Registry change.
While it is pretty common knowledge that people with messy desks are more creative, and my desk can be pretty messy whether I qualify as creative or not, I still like the "Tidy desk, tidy mind" idea. That applies to software as well, as far as I'm concerned. If an application leaves lots of Registry entries behind when it is uninstalled, it makes me question what is going on in the application itself, and how competent the programmer is. (Sorry)
Most Anti-virus providers have had to build special "uninstall all our stuff" or "clean up our Registry settings" utilities at some stage or another just to stop their software from breaking Windows, their own application, or other applications. Usually in response to the new category of third party "Uninstallers" that did more harm than good, mostly.
It is just good etiquette to clean up after oneself as well. Microsoft certainly encourages it. But sure, there is no direct revenue in it.
Of course, there are a few common Registry entries between MC versions, such as DirectShow filter registration. That just complicates the issue.
As an intellectual exercise, search your Registry for "Media Center 23", "MediaCenter.23", "mc23.exe", and "mc23". Then change the version to say 20, 18, or earlier. You may be surprised. Some of it is Windows caused junk, like mime types, but even though I have cleaned up the main Media Center entries for old versions, File Association records are still in there going back to the first version I installed, MC18.
Anyway, File Associations are a bigger issue for me.