If you look at the bond market, which filters out all the noise, you can basically see there is no panic. These guys know a lot more than the average American and they're reaction so far to this looming deficit is, "meh."
Granted Congress can surprise the market, such as when TARP was not originally passed and we saw a 900-point intra-day plunge. However, the current sentiment seems to be overwhelmingly that something will get done.
Perhaps you are forgetting that a bulk of the US bond market is funds that mandate investment in only AAA-rated securities. There are only a handful of nations that have AAA ratings, and the US is by far the biggest and most liquid. So it is fair to say that bondholders have gotten themselves trapped. Many funds simply can't move out of the US bond market, and they'll go down with the ship - or they're bail the moment the US loses the AAA rating.
Bill Gross and the rest of PIMCO, the largest bond fund in the world, have had a somewhat different reaction to the US debt situation than just "meh." It is not a "meh" situation.
Your first two sentences make the argument that bondholders are trapped. Your third sentence then says they may bail if the US loses its AAA rating. How can you "bail" if you're trapped? That's rather contradictory.
Gross has made it very well known that he's short Treasuries. So? If the bond market is expecting a default, technical or otherwise, it would be priced in the yield. The yield in the market at the moment is giving a "meh" sentiment. You want to see a bond market that looks concerned, look at Greece or Italy.
Edit: Let me qualify this post by saying that by no means do I think the US's indebtedness is not a problem. It is a rather severe and potentially catastrophic problem. When I say "meh" I mean that specifically towards this August 2nd deadline in which we are heading. Short-term the bond market is shrugging its shoulders. Long-term, we do have a very real problem on our hands. Just to be clear.