Personally, I feel that there is no need for clothes that are more comfortable than normal on an airplane. I typically wear jeans and collared shirts in my daily life, and I don't need to wear different things just because I am spending a few hours in an airplane chair. And I am 6' 5" so probably less comfortable than most on an airplane (though I am only barely overweight so maybe more comfortable than average in that respect?).

So, what is the problem? It is a minor problem, but here are my thoughts. In an airport I am surrounded by people who "dress down" for reasons that do not make sense to me. It is undesirable to be surrounded by people who's behavior you don't understand--again, in a minor way. And I would say I would rather be around people who are dressed nicer, so invertign that we get: it is a minor "problem" to be around people that are dressed down.