Small detail, I guess.
Believe it or not, there are several very good, completely free registry cleaner programs out there:
Best Freeware Registry Cleaners Reviewed
Important: "Cleaning" your registry with a registry cleaner program should not be part of your regular PC maintenance. Registry cleaning has been sold as an important task up there with updating Windows and running malware scans. Not so. Registry cleaning is best used as a diagnostic tool when you suspect certain kinds of issues with your registry.