GR4Techie,
Being picky and discriminating against a former condition that is of no problem (if it even existed in the first place) any more are quite different.
If a person fails the flying aptitude tests, or they have a very serious, current medical problem, then I understand. However it is possible to "grow out" of asthma, where the symptoms are no longer present.
I am willing to bet that nobody has ever had the balls to officially challenge the Services on their policy regarding 'childhood asthma'. I have read on here, that apparently Forces medics, and other personnel from not only the UK, but the world over can't understand it either. But those higher up the Chain of Command won't budge....