My experience mirrors this. I dress for comfort when I travel (unless I have a meeting directly on arrival, which I try to avoid), which will often mean a pair of chinos and an untucked flannel shirt open at the collar.

In a good hotel, unless there's a posted dress code for the restaurant or similar, it's not the business of the staff to draw conclusions about you from the way you choose to dress.

Case in point: I was staying at the Westin Palace in Milan a few weekends ago (upgraded from a single to a deluxe double corner room on account of my SPG Platinum status) and decided to have dinner in the hotel restaurant, which had good reviews. I was only staying for one night, on a whim, and hadn't packed anything smarter than jeans and a casual shirt. I got the same service as the party on the next table who were decked out in furs, jackets and ties, and I would be disappointed with anything else.