Air Force/Navy Depate.

[Ivan]

When you land on a planet, take a look at all the ships flying around. Do you see any special ones designed for air flight? No, they are all spaceships. This leads me to believe that spaceship technology has advanced so much that aircraft are obsolete, and spacecraft are used for air patrol too.

This makes sense because;
A: The destruction of Sprague.
and B: You cant kill a ship that can get into space in a few seconds, if yr flying one that has to stay in the atmosphere.

Atmosphere doesn't consist of lone layer, it's hard to define its borders. Some fighters can fly up to space even nowadays.

But yeah, nice example about planet. However I doubt Microsoft guys would bother with models they're not paid for (taxi?...).:P