The publishers had the choice to go with Amazon but decided against it because they made more money with Apple.

So in what way is this bullying again ?

I don't think you understand the concept of price fixing - The intent is that Apple is making the decision for the Publisher's by proposing an offer that isn't in the sense of "pros vs cons", but rather "right vs wrong". Of course most Publishers agreed because it was for the greater good of their company, and the only one hung up with the bad rep is their ring master.

"You can either join us, or we'll collectively squash you."

So, no arms were actually twisted. There was no iBooks marked when the emails were sent and the publishers could've said no.