One thing I've noticed, though: this happens in chain restaurants regularly, but in smaller, independent restaurants only rarely.
It's not really cultural: I think it's a product of the disconnect that naturally occurs when people without any feet-on-ground presence are making policies to be followed by the staff, and the other end of the feedback loop isn't isn't in place.
If I have a problem with the food, I'll get a waiters attention - perhaps with a snap of my fingers - which is expected and not at all rude and let the waiter know.
Snapping my fingers at the waiter isn't something I'd ever do in the US though.
I expect writing to have minor flaws.
I expect a sandwich to be a sandwich.
Mistakes that aren't noticed by the time all the food is handed out should be rare, and there's no problem in flagging someone down in that case.
A reply below you says its to make sure you got what you ordered, etc. I could count on a few fingers the times ive ever got the wrong thing/meal, and then you just ask.