Not it's not. CCleaner just provides an all-in-one interface to tools that already exist in Windows. It's a convenience program more than anything.
And what are the criteria it uses for determining which are invalid entries and which are valid? How do you know that it's only selecting so-called invalid entries? And how do you know that it's not wiping out entries that may be needed for something, only you haven't discovered it yet, or you attributed it to something else?
The registry is another thing most people should pretend no longer exists. It's not this mystical black box full of secret undocumented performance enhancing settings, or really anything that remarkable at all. It's really just a pretty boring, and poorly implemented at that, flat file database for storing metadata. Seriously, a first year computer science student should be able to come up with something better in the course of an afternoon. The thing has existed since at least Windows 3.1, though it didn't see heavy use until Windows95. Since then, in Microsoft's usual fashion, it's slowly mutated as they dump more and more responsibilities onto it. Microsoft is so worried about breaking backwards compatibility, they're willing to sacrifice future progress in its name.
So many people seem to have the same mistaken idea as you, that it actually NEEDS to be "cleaned" or "fixed" when it really doesn't. Others seem to think that it will somehow improve performance to "clean" it, which is also patently false. Any given registry entry is all of a few bytes in size. So you'd have to prune tens of thousands of entries to reclaim a single MB of RAM. And the RAM -> CPU link these days is so fast, that finding any given entry in the registry happens in the space of an eye blink. It's below the human threshold of perception.
So yes, these programs ARE snake oil. When you take a few moments to step back and actually analyze their claims -- what might be considered due diligence -- you find that there's really nothing to them. They're feeding you a bunch of half-truths at best. It seems pretty clear that you don't really have the necessary understanding of the lower level functions of Windows to really be able to do a critical analysis of these programs, so it would seem tactically unwise to be proclaiming their virtues. Merely accepting things because they sound technical, and you do not want to appear ignorant is not a good long term strategy. Though repeating that incorrect information is an even worse long term strategy. Sooner or later you're bound to run into someone who will see it for the BS it is.
And Cnet is quite frankly something of a laughing stock in the tech community. They cater to the Dilbert PHB types, which is a perfectly acceptable business strategy, but it's not going to gain you the respect of the intellectuals of the community.
Ultimately most people tend to fall into one of two categories. There's the people who just muddle along through life, learning as little as possible about things like computers, content with simple answers even if they aren't always technically accurate, and those are the people who Cnet is gearing things towards. Then there's the curious types, like me. We have an insatiable sense of curiosity about pretty much anything and everything, and we devote our lives to learning as much as we can about as many things as we can. We are not content with Cnet, because we very quickly learn that much of what they say isn't true. You could call it good enough for government work, but we want more.
It's a perfectly acceptable business strategy, though one that doesn't seem to be working overly well, but it does not make Cnet an authority on anything.