I think this is backwards: it was the book publishers (and Apple) that were sued for colluding to raise e-Book prices and had to settle -- which is what anti-trust laws are meant to protect consumers against. Amazon using its size and some questionable tactics just doesn't fall into that category.
The book publishers have done a great job painting this as a David vs. Goliath story, but it's really two Goliaths battling over a shift in publishing and distribution.
Just because it was illegal for book publishers to collude with Apple to fix prices in the ebook market to their advantage doesn't make it any less illegal than it otherwise would be for Amazon to leverage any monopoly power it may have -- as that is legally defined, which doesn't require a complete absence of competition -- in the online physical book retail market to acheive market power in the ebook market.
The book publishers have done a great job painting this as a David vs. Goliath story, but it's really two Goliaths battling over a shift in publishing and distribution.