I just got back from a three week work trip to APAC that I added a small drive trip to the end of, flying TG BKK-HKT time in the air is about 55minuntes and we had some pretty good turbulance on my return and they somehow managed to serve a meal, drinks and an after meal cofee/tea service plus a warm towl both before and after the meal. This was on a 747 (though sold as Y/C) the F seats were full and there looked to be another 15 or so seated in C (bummer for them as the TG F seat is sure nice). To say that DEN-LAX is too short to accomplish a meal service is just false, it can be done though I never saw the TG FAs not doing something related to service (ie reading, talking etc). If the captain made the judgement that it wasn't safe then there should have been an announcement then people such as to OP who expected to recieve a meal would have had their expectations set properly.
To just pretend like it wasn't a meal flight however causes one to wonder why and if it was a good reason I can't see why they wouldn't tell the pax, this way if someone complained they are covered: hey we told the passengers we couldn't do meal service because the captain said we needed to be seated.