The most dramatic event in publishing in 2010? That's easy. It was the face-down between five of the six biggest publishers in the US and Amazon over trading terms in the ebook marketplace: the shift from wholesale pricing to agency.
Even in theory, the shift was complicated. Publishers' established prices went from near-print to about half-print. Margin offered to the channel was reduced from 50% of the established price to 30%. Control of pricing shifted from the retailer, who could charge whatever it wanted in the wholesale scenario, to the publisher who required the same price across all consumer touchpoints under agency.