Reskins, reskins and more reskins. Same shit given a new cover and sold to us as new. That's what 10m+ subs get you.
And Kil'jaeden at the Sunwell was really him. You could argue that he hadn't come completely through the portal, but I don't see how that would affect his power. Maybe he was sucked back through before he could bring his full strength to bear. I'd still put him below Old God level.