This is my experience as well, although on Royal Jordanian and Emirates, they actually have in flight cell phone service. Few people bothered to have their phones away, much less off, and nothing happened. And these are on Boeing & Airbus aircraft, the very same ones that United & Delta are using.

I hope this rule does change. There's simply no reason to yell at people to turn cell phones off anymore.

The last flight I was on, there was a guy taking pics with his phone during take off. Nobody noticed.