The practice of referring to, say, you as a "person with asthma" as opposed to an asthmatic is called "person-centered thinking" and it's a very real part of the professional culture of the mental health care field. Calling you asthmatic would also be considered a faux pas in this culture. It's less about not using perjorative terms than preventing the creation of those terms to begin with.
When I mention this, I say that I am autistic, because it's a major part of my personality and identity. To say that I have autism would feel like I was talking about an affliction. But it does make sense that health care professionals would phrase it otherwise. Having been treated for depression on many occasions, I know that they typically use phrasing that at first seems strange but is designed mold the relationship between carer and patient in the right way.
$.02
ETA: And of course it turned out others (lurkylurk, mikmaxs) had already said the same thing, only better. Take it as me voicing agreement.