I worked for a few months at a convenience store(worst job I ever had), and my experience was that the only people who usually got upset about getting carded for booze or smokes were the ones who were underage.
I'm 35 and I still get carded occasionally. I always thank the clerk or waitress loudly and sincerely and tell them they'll never hurt my feelings by asking to see my ID for a beer. I don't know why the seller should be embarrassed, or the buyer should ever get upset if they're old enough(although I've seen a few jerks who do get bent out of shape), and the older, the better! ;)
It's not just the restaurants that get fined, the servers and bartenders can face fines and/or jail time. I personally would rather look at someone's ID and take a few minutes of grief than spend a night(or more) in jail. Besides, I find it can work in my favor...nobody tips better than a fortysomething woman who has just been carded!