First yelling commands would just be .... awkward. Utilizing the touch screen is much faster, intuitive, and neighbor friendly
Second for the split ground/air:
As mentioned, vision would be a big playing point.... some *speculation* on my part:
1) Climb/Descend above the clouds (takes a turn)
2) High alt removes you from range of ground anti-air units
3) Can't Fire on ground units or low level air units (from up high)
4) Higher visibility at high alt in fog of war both in the upper clouds (for other units) as well as some on the ground. So say a copter at high alt would still see some ground space directly below it, while being out of vision range for ground units. Practically like having a spotter for your ground force in FOW. Also, air units at mid level could have vision ranges for both ground and for the higher altitude. However, if an aircraft is sitting at the mid layer, it's vision of the higher layer isn't as great as if it were up there itself. Fuel consumption would be different.
5) Captured cites act as a kind of radar, they can scan see a small area directly above them in high alt space only. Also has the benefit of making it harder to sneak up on a base (where there tends to be a lot of property). You'll have at least 1 round notice before they descend and try and spread havoc.
6) Air Drop Infantry (Even more reason to have fun with Sami
)
Wow, how's that for a semi brain-storm....
You can think of a lot of things.... what makes AW great is that it seems to always get the right level of common sense and detail, in one nice easy to use package. This game will more than likely own the initial wave of DS games. (assuming it comes out relatively early)