Except we're not talking general content. The maps are cool incentives. Getting a credit from the retailer to a DLC download is a cool incentive. Leaving out CORE FUNCTIONALITY if you don't order from a particular retailer is not an incentive, that's a pretty poor business decision.
This is also not "wanting everything for nothing". I want to have access to the same Civs that everyone else that paid the same amount of money I did. If I spent $50 and you spent $50, we should have the same core features. Now granted, your retailer may have given you a DLC credit which I would have to pay for, that's fine by me, that's incentive. You may have a few maps that I don't have, also fine, the core feature is the random maps, not the pre-generated maps.
But you have Babylon and I don't because I bought it off a retail shelf and you bought it digitally, even though we paid exactly the same? That's a core feature I don't get while buying the same thing at the same price. That is the problem, not a sense of "entitlement".
Now if it were the Collectors Edition, we might have a whole different debate going on. When one person is spending $80 and the other is spending $50, you'd expect to get more for your money. But at the same price?
What you're arguing is unrelated to what people are making the complaint about.
Edit: Example time. You go to Loews, I go to Home Depot. We both buy the same Power Drill for $50. You would expect both Power Drills would be functionally the same, and in fact identical Power Drills. Let's say Loews had a sale (incentive) and offered a cigarette lighter adapter with it. I have no reason to complain, because functionally, our Power Drills remain identical. Now let's say that the same situation happened, but since I got it at Home Depot, it did not come with a power cable or battery in the original retail box, but the one at Loews did. For the same price. I would have every right to complain about the business practices being involved here.
Alternatively, if I spent $50 on the Power Drill I bought at Home Depot, and you spent $80 on a package at Loews, and yours had all the power cables and batteries and mine didn't, I would have no right to complain, because you spent more money and got a superior product package for it.
The first one is what people are complaining about, the second one is what you're arguing against. It does not apply here.