Irrespective of the rights and wrongs of concessions for disabled people, there is no mention of a concession being anything other than over 65s and students in last years season ticket announcement so it is strange that you got one however it doesn't surprise me.
Season ticket prices frozen ? Accrington Stanley FC
Some clubs do concessions for ex servicemen with a Defence Discount Card, Stevenage did for me last year when I asked and they also did the same with season tickets. From memory Rochdale charged the full price for disabled last time I was there except for those in wheelchairs on the basis that they could choose any seat they wanted where as wheelchair users were stuck at the front.
There is no such thing as a disabled person per se there are people who have a disability and that may not always be constant. As Chris says just because he looks fine when you see him it doesn't mean he is always fine. I work with the Council team which deals with helping people claim benefits, apply for blue badges and assess care charges. Everyone is different and some disabled people get paid far more than the average wage where as others don't and can receive very little so to to base having a concession on poverty is also wrong. On the other hand the same could be said about pensioners who do get concessions regardless, however it would be wrong to means test season tickets.
My personal gripe is as I have stated above regarding flexi tickets and I discussed this with David Burgess at Carlisle and emailed him as requested so that is my crusade!