Although too some extent I agree, I also believe it is a matter of perspective. What appears to be dressed up for some is only so because that's what were accustomed to when we imagine 'dressed up'. Suit and tie isn't intrinsically, or perhaps absolutely, 'dressed up' nor are clothes that some see as 'slobby' intrinsically slobby. Its all a matter of what our society perceives it to be. We're taught that suits are formal and t-shirts are casual. Now imagine a world where people were taught that t-shirts were formal and suits were casual. Being a slob would mean putting on a tie.

I once wore a toga (a real toga, accurately constructed as the Romans would have, not a bed sheet) to a formal dinner (it was a Classics dinner at school) and some people made comments that I was dressed inappropriately, and perhaps they were right. My reasoning, however, was that 2000 years ago, the toga was the equivalent to the modern tuxedo. So, by some standards, I was 'dressed up' much more than most of the people even wearing suits.

That's my take on it.