We’re not going to see the iPad hit stores for another two months, but it is already changing the ebook game and forcing publishers and consumers to pick sides.

Last night, several blogs including Venturebeat and NYT’s Bits Blog noticed something was amiss on the website of the world’s largest retailer: Amazon suddenly stopped selling books from Macmillan, one of the world’s largest book publishers.

Not every Macmillan book is gone, but popular ones such as The Gathering Storm are no longer sold by Amazon, either in physical…