Back in the 1990s, when I flew a lot on UA transpacific and transatlantic -- in business class -- I found I would be very thirsty if I declined wine with the meal and coffee after the meal (I don't like to drink alcohol while flying, and I don't drink coffee at all). For whatever reason -- and this was unique to UA -- substitute drinks (like water and Coke) were not forthcoming, even if I asked for them. Since I'm a window seat person, I often had to ring the call button to get a drink (especially on transpacific, where the flight attendants disappeared for hours on end).

Never had anything like this on any other airline where I've flown business (Swissair, Delta, Air France, American, Lufthansa, Finnair...). I don't remember using the call button on any of those.

It was one of the big reasons I dropped UA for DL.