When I first started with cows around 2006, I bought a few commercial Herefords from various local sources. I bought 2 older bred Hereford cows from one farmer/feeder operation that was going from cow/calf/finish to finishing only.  One was very gentle, one was the cow from hell. She about broke my arm pushing over a panel when a neighbor and I tried to load her in a trailer.  The best thing about that cow was she taught me early the importance of having a good corral, handling and loading facility!

Her BWF calf was the same way.  I was happy to see both leave, while the other cow has been a foundation for a lot of my current commercial genetics.

I have no doubt handling is a part of it, however it also seems to me that genetics is the basis for disposition.

Imho and limited experience, you can make a wild cow worse with poor handling but even good handling will not gentle a genetically wild cow (or bull). 

This is probably also why the Angus association has added a docility epd.  A good local Angus breeder who treats all of his bulls well and the same has a wide range of docility epds in his upcoming bull sale catalog.