A Question About Current Dress Codes For The Symphony And Opera?

I don't know too much about the USA, but here in the UK it is pretty much do as you please! For example, try and look at the BBC website and the Last Night of the proms broadcast from Saturday. Everything from evening dress to jeans (although, I accept TLNOTPO is a bit different to regular concerts) However, here, dress codes have very much gone away. Time was the evening dress was de riguer for the Royal Opera House, but no longer. All venues are trying to attract an audience and the last way to do that is by being stuffy about dress. I was surprised by the number of answers to the previous question (which I didn't answer) which suggested ladies should wear 'gowns' Surely that is the last thing (a) when they are sitting down all evening and (b) just serves to make concert and opera attendance elitist. Personally, I wouldn't go in T-shirt and jeans, but wouldn't worry about being seen in 'smart casual' like blazer and slacks