Zooming in means I can't see where the major international routes end up. It also doesn't make the dots any bigger.

RTW1, you're right, they might overlap, but only when zoomed out. The problem is, when zoomed out, it's hard to hit the right airport anyway. So I still think that making it easy to select the big airports when zoomed out is better than not making it easy to select any of them. To select a smaller airport just zoom in - they won't overlap then.