I'm using the latest Ccleaner version 4.18.4844 in Windows 10 Technical Preview. And ccleaner is picking wrong windows name and build. MS Windows 8.1 Pro Preview.
Another thing is my notebook has a dual gpu system and ccleaner always pick up the inactive gpu name board.
Both of the issues are not deal breaker, i just wanted to report.
since Win10 is still in (very early) beta stage, I wouldn't expect CC to even consider getting things right with it until it's planned release for late 2015.
but I guess if you report it early enough, Piriform will add it to some checklist.
as to the gpu issue, which slot is CC picking up, the x16 PCI-x one or some other?