I live in a suburban area in the U.S. and what you report is similar to what I've experienced, too.
It could also be that my social circle is older, and many of us are parents, so it's not as convenient to go out for a hard night's drinking.
But even when I'm out in town non-drinkers aren't bullied into drinking. If it's a party and they're not drinking (especially if they're men and thus pregnancy is off the table) someone will likely push them on it because it's uncommon but no more than vegetarians or anyone else with dietary restrictions.
However in that case "I don't drink because I don't like being drunk" or "I don't drink because I don't take it well" is a perfectly acceptable answer. Then again, a lot of the people I'm talking about are goths so straight edge / clean living isn't too uncommon.
Maybe you're driving. Maybe you're on medication. Maybe if you're a woman you're trying to get pregnant (or already are).
Either this "if you don't drink you must be an alcoholic" thing is entirely American or lots of people on HN hang around with the wrong crowd.
EDIT: Also being "on call" is a good reason not to drink. Though if you need an excuse every time you go out with your friends, you deserve better friends.