Why should there be a sharp line between GUI and text interface? In other words, the question shouldn't be "should this typing thing be in a GUI" and should instead be "is this (or when is this not) a good way of launching programs?"
For instance, I'm actually one of the relatively few people who actually really liked Vista, and a lot of that was on account of the search feature of the start menu. I'd have taken it over XP on the basis of that feature alone, that's how much it improved my usability. (Possibly XP + Launchy would have satisfied me, but I discovered it a bit too late to use it much with XP and view it as pretty much obsoleted by Vista+.) For several reasons, I think it's even significantly easier and faster overall to use the start menu search than it is to use tab completion in a typical shell to launch a GUI program.
(And incidentally, this is one reason that I'm almost completely indifferent about Win8, which I suspect you don't see. I pretty much ignore the fact that metro exists except when launching programs, and I launch programs pretty much identically to how I launched them in Vista & 7.)
No one says "hey I actually have to type when creating a document in Word; what gives?!" even though Word is pretty much undeniably a GUI.
I think that in a lot of cases, the same can be said for the start menu. If you're on a desktop/laptop, most of the time pressing win then typing a few characters is just fundamentally going to be the fastest way to start a program. The Win8 problem comes from the fact that in other situations, or if the user doesn't know you can do that, or if they just don't want to type, the start screen is pretty hard to use well.