I don't think I'm alone in stating it should not differ - at least by such a wide variance. Actually, I'm pretty sure the VP of Inflight would agree with me.

PD drinks should be consistent - every flight, every time - unless there is a late boarding/departure crunch or late catering. Inflight service should be consistent - every flight, every time - unless there is a safety issue with FAs moving around due to turbulence.

The crew has been trained to deliver a specific level of service in each cabin based on the length of the flight and the catering being offered.