I'm A Banana
Potassium-Rich
Heh. But yeah, I get your point. I alluded to this the other day in the thread about a dragon's speed. A duck in real life is twice as fast as a D&D dragon, and an eagle is 4x as fast. In fact, a dragon in flight is only as fast as a human sprinter. For context, The Lonely Mt is 30 miles or so away from Lake-Town. It would have taken Smaug about an hour and a half to get there if he were a D&D dragon.
Like the dragon's speed, the fear distance you mention I have a strong feeling is done because they are still viewing D&D combat as happening on a grid as the default. An influence from 4e, where nearly every combat encounter was grid based I'm guessing. Seeing as how you can't have a 1000ft grid with 5ft squares fit on most gaming tables, all these distances and rates were compressed.
I'm not a fan of sacrificing that level of verisimilitude for metagame reasons. YMMV of course.
Personally, I find this very amenable to a DM judgement call, so it doesn't bug me much. When most folks see a dragon, they run, no Fear Aura needed - it's just the sensible thing to do. And PC's, being exceptions, don't need to worry about it until they're up close. And with the speed - it moves at the Speed of Plot when not in a fight, and in a fight, when I'm using abstract distances, their speed is fast enough to basically be wherever they need to be on their turn.