Another factor that is very real is cost.
Simply put, you can build a shorter banked turn than an airtime hill when traveling at higher speeds, as g-force puts riders into their seats instead of restraints, equating to a more "comfortable" ride.
Obviously, coaster enthusiasts want as much airtime as it takes for their heads to explode, but there is a measure of rider comfort and wheel wear taken into account with elements. Maverick heartline roll anybody?
[youtube]http://www.youtube.com/watch?v=guTTVVco1NA[/youtube]
Banked turns are the less intense element, and provide less track, reducing cost of both track build and wheel replacement.
All that being said; the coaster could use a good airtime hill instead of the banked speed curves. But at least it will be the tallest, fastest giga - right?