In addition to providing a sloped typing surface, the keyboard's magnetic strip attachment to the bottom bezel is also touted to increase hinge rigidity when placed on one's lap.
Though when placed on a flat table, one reviewer thought the sloped typing position felt kinda mushy (then again you could just pull out the magnetic strip away from the bezel and lay the keyboard flat in that case).
I'm guessing the extra folds of the magnetic strip area may also allow the keyboard to be folded around to the back of the SP3 with less stress, avoiding the risk of popping out completely (even when using a case)? Though I still wouldn't like to feel the keys when gripping the back, so I'd still pop the keyboard in the reverse way...