Going to weigh in not so much on the trope, but on the practice in real life (as a shooter myself).
Yes, ideally, you use a two-handed grip on any but the tiny pocket pistols. This is for a number of reasons: it's stronger, it's more stable, its easier to handle the recoil, and it gives you better control.
But many people who shoot also
train one-handed, especially people who are training for self-defense. The reason is that you won't necessarily have the time to assume a "proper" stance and two-handed grip in dire situations. Some, especially law-enforcement officers, (who may be or required to also shoot an acceptable qualifying score one-handed with their off-hand) will train not only one-handed but off-hand one-handed
One-handed shooting can indicate any number of things about a character. Or it can indicate nothing at all about them. And there's no "always" about it.
edited 5th Dec '13 7:29:08 PM by Madrugada
...if you don’t love you’re dead, and if you do, they’ll kill you for it.