I have a feeling that the fact asthma medication may/may not improve respiratory function in those even without asthma makes us all suspicious of drug use. It seems a lot of elite endurance athletes take them too, I wonder if that much hard breathing just makes the lungs sore or something. I feel that Galen's peaked in the shorter distances, Salazar noticed this, and now the last kick to the Olympic podium is the Marathon, as a lot of elite runners do after a few years of competitive mid-distance racing (is elite 5k races mid-distance?).
Like a few posts here, endurance/stamina at a given pace can be trained into someone much easier than trying to increase someone's maximum velocity. That's why marathons are popular here on LetsRun, because even with mediocre times, like an 18:50 5k, if you do enough mileage and stamina workouts you can become efficient enough to run a BQ marathon time. Not everyone can break 5sec. for 40yd or 60sec. for the quarter-mile. More people that post here have or have been interested in running marathons than sprint decent times, so that's LetsRun's infatuation with the Marathons.
Maybe Galen's not the best at racing tactically at the world level once the race gets down to 5k and below. I think his move to the marathon is a good move to prolong his career and truly see his potential in this sport. Maybe his asthma medication gives him an EPO like benefit, which goes by the rules only because he truly does have asthma. Maybe a lot of elite runners have exercise induced asthma from the 2-3hrs. of training a day. I'm not a medical doctor though, so don't quote me on that last sentence.