Marathoning must bring a huge stress like no other. As huge of a fan I am I believe Haile when he says he's retiring because he went out the same way Paul Tergat did: Paul Tergat wanted to do the olympics for as long as possible (ran 1996, 2000, 2004, wanted to do 2008 but wasn't selected) and never talked about retiring. He just finally quit, after having a long track life and road/marathoning life once injuries and excuses got too fierce. Remember he was supposed to do the NYC marathon in 2009, and then the Berlin 25K, (and in his interviews he was so excited for them) but pulled out of both w/ injury and then just decided enough is enough. So like Haile, he made an on the spot decision as opposed to saying "this will be my last race" or "last olympics" because he was always looking ahead.
Haile will probably travel like Paul to big running or charity events, but I believe him when he says he is retired.
He's had such a small career as a marathoner. Does anyone think Wanjiru is going to run marathons from age 20 to age 37? 17 years of straight marathoning? Was it the stress of a 20+ year career of running or was it a 5+ year career of marathoning which made him retire? Because if Haile proved that one could set a WR at age 35 in the marathon, then Wanjiru hypothetically could run 4 Olympic Games and then still be able to set a world record after the fourth. UNLESS, however, a marathoner can't last that long, which makes me start to wonder if people thinking young marathoners will burn out soon are right.