About 10 years ago I owned both a Trek road bike and a Cannondale hybrid. I couldn't justify both, so I sold the Trek. I believe I sold the wrong bike. Yes, for bopping around the city and short-distance commuting—say 20 miles or less—the hybrid is the right bike for me. The upright position is better suited for urban traffic jamming, and the thicker tires make you feel more confident over potholes and rough pavement.
But… once I approach 30 miles or so, I really miss the road bike. Not just because it's lighter and faster— which it is—but mainly because of the drop handlebars. The flat bars of the hybrid force you to be in one position, and one position only. After an hour or so, it gets very tiring. Road bars, on the other hand, afford you the option of three or four different hand positions, and even though you may spend very little time down low, riding the drops, it's the variety of positions that make drop bars so great.
Having flat bars is sort of like having to sit in a chair for hours without changing your position. Road bars let you stretch, sit upright, sit down low and everything in between. And if you're like most humans, it's not any one position, but rather the changing of positions, that makes the difference.