I may be guessing here, but I think speccs were invented and accepted before any of the others. I think all are fine, as long as they blend in with the individual wearing them - almost impossible in the case of toupees, which tend to be obvious, and simply highlight the vanity / insecurity of the wearer. Dentures and hearing aids have advanced in technology, and can be made to appear natrual / invisible these days.
i suppose it's kinda similar to how people are more than pleased to help a blind person down the street, but get frustrated and defensive when a deaf person asks them to speak louder. i would imagine it's all about stigma, and what people feel comfortable with, although in the case of toupes i agree that it is the lack of blending in that can be a problem!