Going along with my dad's first theory, this next theory is also true. In general, the nicer the restaurant, the more willing they are to accommodate. Servers in nicer restaurants are used to dealing with a lot of requests. Since they know their customers are paying a lot of money, they want to help and work with you, to find something you can eat.
When I was staying in N.Y.C. one summer, I went to meet a friend out for dinner. He was taking one of his clients out, so he had picked a nice, upscale seafood restaurant. He remembered my allergies, but thought they would accommodate for me. He was right. I was able to get a delicious cut of steak with vegetables, and I didn't even have to worry. The server was very nice about it, and said I had nothing to worry about.
This is not always the case, but it has now happened to me quite a few times, where I have gone to upscale restaurants and had servers be perfectly helpful and nice about my allergies. I guess you just never know!