Some do it for the 3 xper points. More power to them. I've had one word answers on my questions, and if they don't really want to explain why they feel the way they do about said subject, ugh, whatever. It just depends on the person, really. Some go all out on answering questions, some are blunt, short, sweet and the like. And then, oh then, there's the infamous one word answer.
Not on here. In real life if I ask a direct question I get a direct answer. If I ask an open ended question I get a more lengthy response. I would say it is annoying when you ask an open ended question and someone tried to respond in one word. It usually means they are not listening to you, so yeah that's kind of disrespectful.