Bar choice, like anything else on a bike is down to personal preference. Alot of the older long distance riders just started off with drop bars, got used to them and stuck with them.
For me personally, they offer more hand positions and look a bit more elegant. Top tube length does come into it though. A bike with a long top tube that started life with a flat bar will feel more stretched with drops because of how far out the hoods are. That can be sort of fixed with a shorter stem, but as most bikes come with stupidly short stems anyway, your choices would be limited. An inline seatpost would also move you a bit closer to the bar but at the expense of possibly sore knees due to the different seating position.
Ahhhh, decisions decisions...