I have a feeling some people their windows 10 might not be genuine...
Microsoft said happily that everyone could update freely but the none genuine users reported getting ads bothering them.
Got windows 10 on my tablet (had some bugs with it like being unable to get it out of stand-by but the updates seem to do the trick.)
I also got 8.1 on my main desktop, I like both. I am yet to find any ads or whatever.
Even the build in windows 10 recording is decent.