I've read that DiMaggio, after his playing career, was a person who did nothing unless it resulted in a monetary payoff. He trusted no one and was invariably suspect of anyone he met, fearing they were interested in fleecing him.
I don't think he had any need for a pension. He was an extremely wealthy individual. But, it doesn't surprise me that he would coach for two years to get an MLB pension, which was peanuts to him. Remember those Mr. Coffee TV ads? They paid him serious money:
http://www.youtube.com/watch?v=SUB6LBsveH0
"Joe DiMaggio: The Hero's Life" (Richard Ben Cramer) is a well-written biography.
BTW, Joe made $100K/yr. in '49, '50 & '51 ($952,381 in today's dollars). That was the highest salary in MLB at the time and not chicken feed by any means.
Edited Jan-17 by BeaneBall
Edited Jan-17 by BeaneBall