Contrary to what many people think, punching power isn't the last thing to go on a boxer, it's their egos and the foolish belief they can compete when all the facts say that they can't. It's like some sort of Greek tragedy or something when a fighter is forced back into the ring because of bad business dealings. There's usually only one way it goes after that. That's the truly sad part a lot of fans turn an almost blind eye to. Folks don't want to see what happens to their heroes when the lights have stopped flashing and the interest dies down.
A lot of athletes have no concept of how to manage their fame or money when it comes down to it. So we get what Roy Jones is doing, fighting on in spite of the fact that he's well passed his prime. By any sane estimation what he's doing is utterly insane. He doesn't have a chance in the world of accomplishing his goal, more than likely he'll take even more punishment than he's already taken since his reflexes went South.
Boxing's a brutal business where the margin for error is very small, both inside and outside the ring. All fighters like Jones can do at this point in their careers is make a mockery of previous accomplishments by fighting on and turn themselves into a laughing stock.