It is worth noting in all this that the various pro leagues do have pension funds in an effort to ensure that players have something they can get in retirement. It varies greatly from league to league and your benefits are reduced if you try to take them sooner than 55 or 60. The NBA has a fairly generous one (Hockey is terrible, NFL is ok). Iverson, who played something like 15 years in the NBA, is probably looking at a pension benefit of around $100,000 per year once he turns 55. So, he's got that to look forward to.
MLB has a really generous pension plan, from what I understand. I believe a guy who plays 15 years in MLB would be in line to make around $140k per year once he turns 60.
The best though is the PGA Tour. Its pension plan is based on performance with bonuses for cuts made and earnings and stuff like that. I have heard that Tiger Woods will be in line to get more than a million dollars a year from his PGA Tour pension plan when he turns 60... of course, he will likely have earned well over a billion dollars at that point so I doubt the million a year will matter much to him. Even AI would have trouble throwing away the money Tiger has made (though a divorce !!!!HALF!!!! can eat into your bank account awful quick).
-Jason "my bet is that AI has some illiquid investments and is not totally broke, but he has serious cash flow issues right now" Evans