Taking the asthma point up... I think that demonstrates the essential point, which is degrees of 'affectedness'.
DD1 also has asthma (and in fact has been far closer to dying from that than from her food allergies, to date, touch wood, etc).
However, I wouldn't consider her asthma makes her disabled, and I would think that her allergies do (in a relatively minor way, obv. compared to a paraplegic etc).
But that is because a) her asthma is very well controlled at present, so she generally just has her preventer inhaler and the occasional reliever, but otherwise lives her life quite normally in that respect and b) her asthma is not triggered by environmental factors, just by having a cold, so there isn't anything that anyone else can do to help or hinder her getting an attack.
Whereas her allergies (dairy and egg) are in almost everything, and until recently had contact reactions so she couldn't even sit in a coffee shop drinking water without breaking into hives. And she's lucky, if it was wheat, and soya, and celery, etc etc... life would be beyond difficult.
It isn't that clear cut, once you get beyond physical disabilities, as you need to judge degrees of affectedness, and how constant the problem is. If you are an adult, in control of your own life, with just one allergy, then maybe it isn't such a huge deal. But for a child, who has no choice but to go to pre school/school and eat there (and be amongst others eating there), and trust in the adults looking after you, then it really can be.