In the old days (70's?) you could usually order a limited slip axle (GM Gov-Lock, Ford Traction-Loc, etc.) with just about any axle ratio, although when buying something a little more exotic (like a Detroit Locker) you would have had only a few choices. For example, Ford only offered the Detroit Locker in 4.30 ratio in Mustang and Torino, while I believe Traction-Loc came in 3.25, 3.50, 3.91).
In today's world the car makers reduce cost by keeping fewer parts on hand, so they limit your choices. I think they assume that you buy a limited slip for towing, so it goes along with a lower ratio.
Bruce