Don't buy the Amazon propaganda. They want to monopolize the market and have publishers subsidize the Kindle. Macmillan wants to have the flexibility to price books at $15 when they come out, then lower them all the way down to $6, much as they do with hardbacks and paperbacks today.
Here is an author's take on the dispute:
Amazon, Macmillan: an outsider's guide to the fight - Charlie's Diary
I agree that pricing is way out of whack for DRM crippled books, which are only worth about 20% of the price of a hardback because of the restrictions and inability to resell them after reading them.
In any case, Amazon's delisting (censorship) of Macmillan paper books is utterly unjustifiable and unacceptable.