[zdragnar]

Entrenchment is an issue in markets with a high barrier to entry, or one where the barrier can be shifted arbitrarily by the dominant player.

Retail isn't really that high, if you count anyone who chooses to open up online, and value additions other than price- shipping policies, returns, service and so forth- are important.

If Amazon drops prices to a significant loss on a single product to specifically undercut a new competitor, that might be an issue. Running one side of a business at a loss and propping it up with another is quite common, though perhaps not at this scale. Either way, splitting it now could only harm customers.