I don't feel they are necessary, even for less advanced users. Apple do a reasonably good job of keeping things safe and up-to-date.

The number of users may also reflect their pushy "you need this!" marketing. I installed MacKeeper a few days after switching from Windows to Mac, as I had no idea what I was doing. Ended up uninstalling it, then reinstalling OS X from scratch just in case.

That's what I thought, thanks. I'm a newish Mac user, so I was a bit confused by the whole situation, since other Mac I know told me not to install anything of that kind.

If you stick to official software and don't care to scan documents for windows viruses and such, you won't need any antivirus. I do however use CleanMyMac 2 to remove stuff I don't use, this is the only piece of "cleaning" software that I think is actually worth it. I like how it helps me getting rid of logs and language files in a lazy way :)

Not usually, but a lot of users coming from Windows just reflexively install a cleaner/AV anyway.

Cool. I'll stick to the "no cleaners" personal policy then.

The thing is, those apps aren't very useful at Windows either.

Get to any Windows user, and ask him when was the last time his anti-virus stopped him from doing anything. Malware has adapted since the 90's.