This old catalog has large crosscut saws (sold by the foot!). They all have a rounded "belly" on the business side and I'm wondering why.
My best guess, without just googling it, is that it widens the last strip of wood thus reducing snap offs.
This way the weight of the saw and therefore the cutting force will always be concentrated on a small number if teeth, which are able to slice deeper thanks to the extra force. Remember that when crosscutting you need to slice wood fibers. Rather than shear them as you do when ripping.