Last time I checked you still had 18 other leaders to play in Civ 5 right out of the box (or Steam, whatever you prefer). I don't really see how not getting to play Babylon would degrade your Civ 5 experience to the point of not wanting to buy the game....
I guess you will probably be able to buy Babylon in an expansion pack at some point.
On a general basis I would say there is a surprising amount of whining on the forum about the price of the game - be it the standard edition, the deluxe edt. etc.
Personally I spent about $60-70 totalt on Civ 4 with expansions over the years, and I guess I've clocked a good 250-300 hours on the game. It gives a price of just over 20 cents pr hour. And I expect to get the same kind of value for money from Civ 5.
I would have paid the extra, and I would buy Babylon now, but it is not even offered. To me that is ridiculous. The other thing that irks me is that there are no official mods added to the game, like the had for civ 4. It seems cheesy, everything changed with this steam garbage, and no worldbuilder, no modding. They should have made a retail deluxe edition. People will pay, and we all know they need the money.
So far you are going to be hard pressed to gain the respect you got financially from civ 4, by playing civ 5. The reason why, control of the game we paid for has been taken completely out of our hands, until that changes thats how I am going to feel.