8' is standard Loewenberg practice. However, 8" is not nearly enough depth for mechanical systems and structure. Plus, in any high-rise you're gonna have lobby spaces, basements, and mechanical floors that require more than 8' of clearance.
I'm guessing the height figure is suspect. Perhaps they're measuring from Upper Wacker - in which case you need to add ~70' to get the height from grade.
EDIT: If the rendering below is accurate, then the 8'8" figure is close to correct. The door out to the balcony should be roughly 7' tall, so the transom above it is only about 1'. It looks like the mechanicals are placed into the partition walls, like a cheap motel. The wall separating the living room from the bedroom is a whole glass panel wide, so possibly 30". Of course, doing that enables the floorplates to look very very thin from the outside, which is desirable with a glass system.
