I agree this is a nice tradition. I must say, though, that in my first year here, I can count on one hand the number of Captains who offerred to buy dinner.

I do think that if the Captain suggests that the crew go out to an expensive restaurant, knowing the FO and/or SO are on new hire pay, he should make the offer to cover the dinner. There's a sort of expectation, and desire, to spend time off as a crew. I think some Captains forget that not all new hires are drawing a military retirement.

As far as tips are concerned, I'm embarrassed when I witness a Captain give a measely one or two dollar tip to the cab driver on behalf of the crew, sometimes three of us. In some countries, that tip consititutes the better part of his pay. I prefer to tip myself.