The WebRoot is targeted more on users that want an antivirus protection, while CCleaner is a system optimization and cleaning app and with the right mod (CCEnhancer) can be a powerful cleaning utility.
I've checked both apps and I must say that CCleaner is installed by default on all my computers because it gets the job done by cleaning registry files and temporary files.
I am not saying that Webroot is bad, but they're just two different applications that offer various features.
