Apparently nobody's mentioned this here yet, but the Bits blog post has been updated. According to the blogger's colleague who spoke to someone at Macmillan, Macmillan wanted Amazon to go to an iBooks-style agency-style deal, where they got to set the price and got 70% of the take—or else Macmillan wouldn't give them the e-book for 7 months after it came out in hardcover.
Covered it here:
http://www.teleread.org/2010/01/30/n...ks-style-deal/
Bear in mind that, as Cory Doctorow said, just because Amazon wants to charge only $9.99 doesn't mean they're your friend.