It's an interesting question, I wonder what his criteria is. The one that really sticks out as being out of place for me is actually Epicloud. There are 5-6 Devin Townsend albums that I would be more likely to call prog rock essentials than Epicloud.
As much as I love Epicloud, I agree that he has quite a few albums considered more essential/definitive.
I wasn't around back when SFAM was released (well, technically I was, but I have no way to assess how it affected the scene), but I have a certain feeling that SFAM actually did stir up the pot with regards to the progressive metal scene in a way that TSOAD did not, but please correct me if I'm wrong.
Dream Theater was more popular then than Neal Morse Band is now, so it naturally reached more people, but both albums were pretty much universally loved like crazy by the respective fan bases (INB4 a dissenter to ether album chimes in otherwise
). Besides, a book like this is naturally going to tilt a bit towards the author's likes and dislikes (if I were writing a book on the classic prog of the late 60s and 70s, I might give Gentle Giant a sentence or two at most
), so I am guessing the writer is a big Neal Morse fan, thus its inclusion despite the album not quite being a year old.