It's not that Wayland needs X: it's that it can't replace it.
To replace X, Wayland needs to be properly network transparent. The Wayland devs have no intention of providing network transparency. (At least if thier FAQ is to be believed).
So Wayland can't be a replacement for X; it's more like a better DirectFB. Bolting X into Wayland is as transparent as running X on Windows or Mac- which means not at all. Bolting X onto Wayland doesn't replace X either: it's continuing to use X.
I have no problems with what Wayland does; but calling it an X replacemt is an insult to both projects.