It's like the App Store. Things get disapproved occasionally for unknown reasons. Like the App Store, most posts make it through, but some submissions are rejected while other similar submissions do not.
I think I may have accidentally left some extra URL junk on the end, from my feed reader, but that's the only thing I could think of. I tried resubmitting it without that and it seemed ok, but then I got rid of it, thinking that if indeed it irked the powers that be, best to not insist.