Jack Johnson Boxing vs. Current Boxing

I always wanted to comment on the fact that in the Jack Johnson documentary, I noticed how his fighting stance is COMPLETELY different than the one that they teach us in Martial Arts, his stance would be considered exactly what you wouldn't want to do. Without disregarding Johnson's skills, I must say that now a days, we are required to "keep your hands up" and close to your face and lover your chin in order to prevent any serious damages, like a knock out for example. I was surprised when I saw that not only was that how Jack Johnson fought, but every single boxer fought that same way. You could say that even fighting sports change over time. (:<