Prog does not groove?

Well, what I meant was that it's so groovy that one (at least I) can't believe it's in 9/8 at first glance. Its because of it's "fake simplicity" that mainly comes from the low amount of notes used I guess. So back when I only loved listening to Supper's Ready and wasn't too familiar with all the parts yet, I always fell for that one and started to feel the groove in 4/4 and then stopping every second like "wait, what happened there?", then begin to groove again and repeat :D (well ok, I didn't repeat it every second but you get my point). It is a deceptive groove in a way, which I why I chose to call it disturbing. Whatever one calls it, its deceptive quality is what makes that certain piece so unique imo. 

P.S. Even though I am an amateur musician I often have a hard time figuring out time signatures in songs, this might be a reason why above applies to me to a greater extent than others.