Just read the manual online and it only mentions including a 20-pin cable. I also quite often see pics of motherboards with a 24-pin socket with 4 of them covered up by a yellow sticker.
I thought I was pretty well-versed here, but I'm apparently slightly confused. Perhaps my questions will be answered when I actually receive the PSU. Sounds like I might need to send it back and exchange it for "BTX" though.