Actually it is not that uncommon at all to see two lenses that close in focal length, many of the medium format companies do this, the 80mm is what is normally considered the normal and is used as a kit lens, the 110 often times is used as a people taking lens, the small amount of extra focal length, allow you to step back a bit and not have the big nosed look to your frame filling head shots.

Heck if I remember right Mamiya has an 80, 105, 110 and then a 150 in their lineup..