I found that too, Occam. I like how it keeps the brood sealed, but they are harder to separate. The reason behind it, as I understand, is that gaps are not needed because the hive is not vertical, and the bees don't need to pass upward into another box.
I know some beeks use frames with a gap in between, like langstroth, but then they lay a cloth square over the top on the hive, which can be peeled back as needed to expose frames.