The key difference is, as Chris said, that the tip overlays on the back side of the bow are made of a material that is stronger than glass and can take the pounding that low stretch materials give it. Generally, linen Micarta is used.
Micarta is a trade name, so if you try to order it from Bingham Projects or other raw material supplier, it may have another name.
Also, the epoxies used in making bows today bows is superior to the glues/epoxies used on older bows and can stand more punishment.
Al (Als Decals)