The model of charging per site was removed in [4], the "low tier" $9 per site was also removed, maybe it was not differentiated enough from the free version to be worth the effort. It also seems they introduced "paying per user" in between [3] and [4], maybe that was a form of substitute for the removal of the site limit.
Disclosure: I am a founder of a cloud hosting startup called Sourcevoid, that's in part why I think looking at pricing and packaging of hosting services is interesting, but thought others might like seeing the links above as well.