What happens is that for the most part, the fighters that aren't worth remembering.
The ones that are remembered are remembered for good reason, and over 100+ years, it's likely that there are going to be much better fighters over the course of that timespan than all at one time, today.
Obviously someone is out of it if they're saying Jack Johnson is going to beat the Klitschkos.
But not so much if they are saying George Foreman would.
You get what I'm saying?