Very interesting move, considering that not all Android Apps can run on x86. This is either Samsung's #1 or #2 tablet, so it's a significant risk.
My theory? Samsung wants a little experience making a high volume, low cost x86 tablet so that they get Silvermont right. Presumably they'll be able to share a lot of design work and parts between the Android and Win8 versions.
It's likelier that Samsung has an internal problem producing enough of its own whatever SoCs to cover all markets they want to adress. Note that they haven't picked the highest end Clovertrail+ from what I can see.