it actually is available on amazon but D2D has the best pre-order bonuses right now and i don't think you can cancel from there.
i wonder what sort of discount or DLC inclusion there would be if one waited for the steam holiday sale to buy civ5.
I'm thoroughly confused about the bonuses now, after reading your last post I queued up Steam to place my pre-order and then for the sake of it checked out the civfanatics forum and found that there's different bonuses:
Map Pack: Cradle of Civilization: Asia
"The Indus River valley was home to the early Harappan civilization while the Yellow River valley in China saw the rise of the earliest Chinese dynasties. Both these regions would be included on the same map (which would be dominated by the Himalayans and jungles of SE Asia between these two fertile zones)."
Map Pack: Cradle of Civilization: The Americas
"Although civilization blossomed later in the western hemisphere, the region from Peru in the south to Mexico in the north was just as important as an incubator for the development of ancient cultures. This map would span this rugged area of jungles and highlands."
Map Pack: Cradle of Civilization: Mediterranean
"The period of Classical Antiquity saw the rise of city states from Phoenicia, Greece, and later Rome and Persia. Their struggles all centered on the great sea in the Middle of the Earth, hence the name Mediterranean. This map will cover the entire Mediterranean basin including the nearby peninsulas and coasts where these great empires grew and prospered."
Map Pack: Cradle of Civilization: Mesopotamia
"The pack covers the traditional Western and Middle Eastern "Cradle of Civilization". It will include the Fertile Crescent with the Nile River valley to the west and extending east down the Tigris and Euphrates river valleys to the Persian Gulf. Leaders will be able to explore new terrain, cultures and conquests."
Babylon Civilization with leader Nebuchadnezzar II - Deluxe download only, not confirmed as DLC
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It's a Steam based game and even if you order it off Steam you don't get all of that bonus content, wtf gives?