Looks like the FTC, DOJ, and the EU are monitoring the situation and deciding if it's worth a full investigation. The antitrust possibility is mentioned, along with this:
Originally Posted By: WSJ
Apple's condition that its own customers should get the best deal available from media companies could also attract scrutiny. Such conditions, sometimes known as "most favored nation" clauses, can be deemed anticompetitive if they distort pricing.
The Justice Department recently sued a Michigan health-insurance company for allegedly using such clauses to hobble rivals.


I also found this interesting, looks like Amazon's conditions for subscriptions on the Kindle are much worse.

(from here)