I have done 6 short-haul flights this year on UA/UAX - 25-45 minutes in air time.

UAX Skywest CRJ-700 2 class (2 FAs) did not have drink service - 26 minute flight - that is acceptable. The woman in front of me powered up here PC after the ding and when she got logged on, it was time to shut down

UA A319 had drink service - west bound of the 26 minute flight above - I was impressed they actually did it - I was not expecting it after the above and it makes me wonder about the above flight

UAX Skywest CRJ-200 50 seater had drink service on 3 out of 4 - about 35-45 minute flight

Last night, on a 41 minute flight (which probably had 30 people onboard), the FA promptly announced "due to the duration of the flight, there will be no beverage service" and took a coffee and her novel to the back of the plane to read. There was no turbulence or anything. The was my 4th time on on the same flight (East/West bound) but the first time this happened.

Of course, I had to test her. I asked for a water. She got me one but did not seem very happy when she handed me the water. Had she said no, I would have said something to her.

My question is: are there rules/SOP on this? Or, FA can decide what they feel like doing?