Well, if you look at this all the US government is doing is refusing Visas to some foreign nationals, as is its right. Just because traditionally such Visas have been available they are not available by right, but as a privilege. Yes it fits badly with the US government pushing them to buy MD-90s, but politics should always be kept out of commerce (or you get the farce of France and Russia supporting Iraq for monetary gain).
Remember most of the terrorists (the Guardian/BBC still haven't managed to rebrand them freedom fighters, I take it?) who helped kill over 3,000 people last year were Saudi nationals who trained to fly in teh USA. Locking the stable door after the horse has bolted, but it's their stable, they can lock it when they please.