I agree. I'd reserve the right to wear jeans for the POTUS since he's a foreigner, though I wouldn't make a point of it.
Same for the Queen. Even though she's technically my head of state, she's a foreigner and hasn't done anything to command my loyalty.
The key is that I wouldn't go out of my way to dress down for either to be disrespectful UNLESS pressure was applied to me to make me dress to a certain standard. I can be a contrary cuss sometimes!
No, we are talking about judging people's social status based upon their attire. Laura Bush has elegance of style, taste, and manners whatever she wears; Michael Moore is a slob even in a tuxedo.
Rules as to proper attire are in no way arbitrary. They are quite well known and established.
Of course dress codes are absolutely arbitrary and to argue otherwise is ludicrous. They are hardly laws of nature or dictates of circumstance. Being tradition bound doesn't make wearing a symbolic noose around one's throat any less arbitrary than decreeing all senators must wear a toga.