Seems odd to me, Jack. There are sometimes things in the code that are there for building upon in future development. That is why people were able to do some sorta hacky things could get shelves before Kobo released them. I could speculate about why this might happen, but it would be wilder speculation than I am comfortable doing.
Did you try syncing to it? I can see that some folks, with a huge number of books purchased from Kobo might want to be able to store some of them on an SD card. (This too is speculation, but not the truly wild shtuff
)