Looking at rewards flights on USAirways, my dates would need 90,000 miles for economy. On Continental I could do the same dates for 55,000. Or fly Business for 105,000. The *A charts say 60k for economy on partner airlines.
If you are using usairways.com, US will not show you partner flights. You must call in to book those.
And the reason there is a difference is US is not showing you the lowest tier of awards on US flights. Given when you are flying (summer), those awards are sold out already.
I would suggest reading some in
this thread and
this.