The EU doesn't need international authority to apply their laws worldwide. They just do it.
But antitrust generally relies on marketshare as a yardstick for market power. And neither Amazon nor the Depository has enough global or european share for even the most paranoid to invoke antitrust.
Note that Amazon doesn't buy companies for market share; their history is of buying companies for their technology, business model, and/or personnel. And for their growth potential.
They also have a track record of allowing their acquisitions autonomous operation, from Mobipocket to Diapers.com. Check here for a listing of some of Amazon's many businesses.
Odds are that, whatever processes and systems TBD has in place to deliver books worldwide (Which may be patented or a trade secret) will be adopted by the various regional Amazon stores. Why license what you can buy outright?