The DU filly was accepted into Book 1 back in June. Granted JustWhistle was probably better regarded then than now, but she the people that assessed her clearly were correct. Yes, they were aided by HotDixie/Bold Union/Gone Astray are running huge in the last few weeks but in the end, they were right to put her in book one.
I hope the decsion to put her in book 1 was made by the same guy that put that $5k GC colt in book 1. They might offset and he might save his job.
As for who's buying, it's the usual book 1 people. Sure some folks that usually buy a notch down (the $75-200k crowd) could have stepped in and bought from book 1, but people at that level may be opting for the conservative route and looking for the "same type" horse hoping that it will now be available for only $30-125,000 or they may have looked at book 1 and assumed prices would be higher, and just not looked that closely into the horses.
At the high end, I guess some people would rather either race or train up to a 2yo sale than take a big loss. These yearlings were conceived in early '07 and the stud deals made as far back as late 2006, so you are looking at the products of some very high stud fees. Stud fees declined in 2008 and dropped sharply in '09, but those with yearlings this year are the ones taking the biggest hit.