I'm someone who buys all my books from bricks and mortar indie bookstores, but I don't understand the uproar.

Look at it this way - if some producer tried to force an independent digital distributor to charge more for already overpriced DRM'd digital copies instead of letting the store set their own prices, who's side would you take?

Why not boycott Macmillan for trying to gouge their customers? Amazon had its own motives for rejecting the deal, but as far as I can tell, neither side was in the right.