Win7 log files are NOT wiped

I downloaded recently the very good free and easy utility tools

LastActivityView from here: LastActivityView - View the latest computer activity in Windows operating system

and

MyEventViewer from here Alternative to standard event viewer of Windows

and run them.

Much to my surprise they show ALL my activities since I setup my 64bit Win 7 system in 2010.

I thought that CCleaner will wipe them because I checked in section "System" the entry "Windows log files"

I think this is a bug.

Why does CCleaner not wipe the log entries?

Thomas