I concur. Histories of prog rock that aren't just either wankoffs to particular artists or lists of albums are damned hard to come by.
Edit: And now I have it. Thanks Rostasi!
http://libgen.gs/ads.php?md5=4a90e69...596790b9509e98
Reading at the moment for research:
Something in the Blood: The Untold Story of Bram Stoker, the Man who Wrote Dracula by David J. Skal. Though I think the description of who he was is a little superfluous in the title. I mean, if you somehow don't know who Stoker was, why are you reading a biography of him? Good so far though.