Originally Posted by glenjay
By "formal" I assume you are referring to opera pumps.
Some manufactures do add a partial rubber heel cap to their opera pumps, Ferragamo is one of them.
I believe the reason for the typical solid leather heel on an opera pump is due to the history of the shoe. The opera pump is pretty much the oldest dress shoe (still worn) in the world. The opera pump evolved from the Court shoe. Court shoes were worn when dressing up to visit the the royal court in various European countries. It is basically just a plain black leather slipper with a bow (or buckle historically). Of course the shoes were polished when going to court. Patent leather did not really exist untill the start of the 1800s.
Because the court shoe has always been made with a solid leather heel (not a lot of rubber products around during the Renaissance), it is considered more formal to keep the all leather heel.
This is similar to the reasoning that was used for detachable collars on formal shirts. Historically dress shirts were made with detachable collars because the collar received more wear than the rest of the shirt, and since dress shirts were/are typically made out of finer materials than work shirts, it was more cost effective to replace the collar than the entire dress shirt.
While I can't confirm your comments as fact, I suspect much of it is true. Way back, there was no alternative to leather. As times progressed, rubber and poly became an alternative. This benefited the maker (cost saving) and user (better wear and traction). The combination leather/rubber heel was developed. That offered the "feel" of walking on leather with the "wear" and "traction" of rubber on the rear of the heel. As that became more practical and popular the solid leather heel became more of a status than anything else. That's why it's featured on special occasion footwear.
Another point is point is how the lift is attached to the base. They are all cemented then most makers use steel fixtures. This can cause slippage because the leather will wear quicker than the steel. As the leather wears you may slip on the nails. Other makers use brass nails. Brass is softer and wears evenly with the leather.