That is true, although I will say that I very often use them at the next connection rather than at the one where the delay occurs, mainly because by the time the voucher is issued the aircraft is often close to boarding and there is no time to go stand in line for take-out or to sit down and eat before takeoff. So a delay at, say, YOW often means I will use the voucher when I land at YYZ or YUL. So I wouldn’t want the meal voucher to expire with the boarding pass because it would render it useless to me.

It would be frustrating to get a meal voucher at 2:10 into a 2:15 delay knowing you’ll likely miss your flight if you try to use it.