The list has strong UK bias for two non-UK-biased genres. That is, a lot of the most influential f/sf works are from the US and those are mostly missing. It's a very university-English-professor list and doesn't appear to relate, structurally, to the genres' internal developmental. (It also blends horror in.) No Jurgen? No Golden Age space opera? No Marion Zimmer Bradley? No Leiber?

Skipping about, I note that the Michael Moorcock choice is Mother London, a good book but easily his least influential in f/sf; however, the most likely for a non-f/sf-reader to have read. Possibly the Guardian cannot send readers to Elric with a straight face.