Is Pink Floyd prog rock?

Yes, and what people don't seem to understand is that both Alice Cooper and Peter Gabriel's theatrics had a direct antecedent in Arthur Brown. Both Coop and Gabriel directly named the Crazy World of Arthur Brown as an influence on their stage shows, with Gabriel telling Arthur Brown before a show (Genesis supported Brown on tours early on), "You'll see a lot of yourself in me tonight." 

So, Peter Gabriel was not somehow "prog" when doing his schtick. In fact, the face paint of Gabriel, David Bowie and Alice Cooper all had a common rock ancestor.

Actually, Killer and School's Out were top ten hits in the UK in 1971-72, and Billion Dollar Babies went to #1 on that side of the pond in '73.  And because of Mary Whitehouse  -- she of the Whitehouse in Pink Floyd's "Pigs (Three Different Kinds)" -- trying to ban the title song from the album for indecency, the song "School's Out" also went to #1 in the UK (Alice thanked her for the free publicity by sending her bunches of flowers). In fact, in Glasgow hundreds of kids broke through police barricades at the airport and overturned limos in an effort to get to Alice. But this whole conversation has been diversionary.

In any case, I am really just pointing out the fallacy of considering one band "all prog" and another "partly prog". My point was about Pink Floyd being progressive rock, which they were. Not partly prog, but a prog rock band on the compositional, sound engineering and conceptual side.

The whole point of the cow appearing on the cover of Atom Heart Mother was a reaction by the band against all the imagery of space pysch rock that accumulated on posters and in articles of the time. They were leaving that era. They were composing full suites of music. They were doing arrangements with brass and choir. And eventually they would release 4 concept albums in a row: DSotM, WYWH, Animals and The Wall -- all different from each other, but all clearly still Floyd. This was no longer your stoned hippy older brother's Floyd. 

But this is about Pink Floyd and not Yes. 

I think this person is trying to imply that prog can't be blues based. I personally don't hear a whole lot of blues in PF. Sure there's some maybe but they went way beyond that.