A clean install of Windows 10 (not n versions) is shipped with stupid game installers for things like candy crush, Disney magic and march of empire which you can remove easily, but not just "hide" with disabling suggestions.[1]
Yes, I meant disabling "suggestions" stops them coming back again in the future. Although Windows has had update "bugs" whereby this setting is ignored. This is solved by delaying feature updates until at least a week or so after release.
ChromeOS is open-source. Last I looked, their build process was a horror beyond all reason. However, it would at least be possible to strip out any advertising built into the OS. Thing is though, Google controls the advertising on the top two pages on the Internet, and as long as that's true, they don't really need to do anything other than make sure you get there. Which is the strategy behind Google Fiber, Loon, and to some degree Android, more-or-less the reason for Chrome's existence, and why Chromebooks are designed around constant Internet access: all roads lead to Rome.
Since Chromebooks are very internet-forward, they get plenty of advertising opportunities without installing banner ads or something similar into the OS. Are you expecting them to start advertising on the Android home screen too?
