Elevation decreases atmospheric pressure, and the difference is pretty small in the ranges that people actually live.

That’s not entirely true actually. At 1.5km (≈5000ft) altitude it’s roughly a 5°C (≈9°F) difference which might not sound a lot but depending on the dish that can double the cooking time. 1.5km is a relatively high altitude of course but not unheard of for villages, smaller cities and also Denver.