I don't think this is really a bug, but ....
I just downloaded and installed CCleaner Free and ran the registry cleaner. Actually, I ran it twice until it said there were no more issues. I was impressed with the speed of the analyze and clean operations.
Just to check, I then ran [brand-X]. It found over 1000 issues. I'm just wondering why.
I would much prefer to use CCleaner because of the speed, but if it doesn't do the job, I'll use [brand-X] despite it's slowness.
While I have moderated the name of competition out, I won't remove this thread as it's an oft asked question and deserves an answer.
I have made generic the opposing product, and locked/stickied the thread. However I hope, fellow moderator, @Andavari will chime in because his explanation of the why of this is much better.
Basically it comes down to this. Cleaning the registry, using any cleaner, is an action that can cause great damage to a PC. Cleaning programs must attempt to identify a registry entry and whether it is still in use by a computer; they rely on the developers of other programs following a programming etiquette that agrees with the method of identification. This (for any registry cleaning method) can result in a number of false postives, removal of many of which may cause the afore mentioned PC breakage.
Ccleaner tends to be regarded (by the internet at large) as a (arguably the most) gentle registry cleaner; while it still does have false positives, they number much fewer than other x-brand registry cleaner software. While you may see fewer results, it is more likely to be actual results as opposed to many that you may actually need.
Also it's likely that some of the items x-brand lists are cleaned in the junk cleaning section of ccleaner (traces, recently used documents, etc).
To simplify what Nergal posted CCleaner has a much gentler registry cleaner and is less likely to cause serious issues.
Aggressive registry cleaners [brand-X] can often find too much and delete something they have no business messing with which in turn means you'll have to reinstall or repair install some programs such as Microsoft Office (aggressive registry cleaning often damages it), etc. That's if you're lucky and it's just a program you've installed on your own, if on the other hand it damages something that's part of the operating system you could find yourself with a broken Windows OS.