I've found that BWI is actually more convenient (with its own Amtrak station in the airport) and quicker to get to DC than the other two airports, especially Dulles which is only reachable to DC by bus or taxi. 30 minutes on the train and you're at Union Station from BWI.

Also, many people actually drive two hours to get to their closest major airport, so it's really not as far-fetched that they'd accept this at their destination as you think.

As one example, those in Champaign, Illinois can depart from CMI (few choices, very expensive), BMI (45 minutes away, also very expensive), Peoria (same), Indianapolis (3 hours away, cheap flights to some places), St. Louis (three hours away, flights more expensive than IND) or Chicago (cheapest flights). Most people in that area drive or take the train three hours to one of Chicago's airports when they want to fly somewhere, because a flight from Chicago will cost $150 as opposed to $400 or $500 from CMI. I'm sure it's the same for people in many places across the US. They may not blink an eye at two hours, especially for such cheap transportation as Skybus.