It wouldn't make sense for dragons to land when they're fighting a melee only character. Why would they give up such an obvious advantage. And to those who don't know, dragons in TES are intelligent creatures and if they're flying around above you for 3 minutes and you're just mindlessly jumping and swinging your sword, they'll know. The only solution I can think of is that the first shout we get will be the "push" one and when we use it on a dragon in the air, it'll disorient them and make them crash.
What obvious advantage, again how could they attack you from up there?
Yes, they could throw things at you, and you could easily dodge them, it's more effective to just land and eat you, or swoop down, which again requires them to be at arms reach so you can counterattack.