What John said is correct. It's designed to protect users, not the pages. The pages are going to be deleted when the rule is made. It's like saying they outlaw meth, but they won't confiscate meth that is already on the market. In fact, they will confiscate is, but you just won't get in trouble for possession. Same mind work with pages, we will delete pages, but you won't get in trouble for creating them before the rule was applied.
Anyways, I see no reason to adress Ex Post Facto, the rule is pretty clear (I should know, having been the one to add it a looong time ago). But this blog did stand out when I saw it. :) Cheers.