I fly on fifty seat UAX jets every week. Most of my flights are scheduled for 90 minutes gate to gate. On the same scheduled time, we have been offered up:

1. Nothing - usually because of turbulence.
2. Water only - usually "flight too short."
3. Water/Soda only, no beer or wine, usually no explanation offered.
4. Water/Soda and beer/wine but no coffee/tea, usually explained as "not working."
5. Full beverage service.

"1" I understand. I can't figure out what the criteria is for selecting 2-5. I have seen all of these offered up on the same 90 minute segment, sometimes with an explanation, sometimes not. Anyone know the current guideline/rules? Is it different for different regional operating carriers?