There is an interesting article on Wired that comments on the rough situation some game developers have to go through because of content restriction applied by certain big retailers, in this specific example, Wal-Mart.

Dominating about 25% of the videogame annual sales in the US, most of the mid sized publishers sure need the kind of exposure a big retailer could give them, even when it comes at a price. Some examples that apply to this would be BMX XXX, Giants and even Duke3D...

However, Wal-Mart's policies go far beyond saying no to a 16-year old at the cash register, say game developers and industry analysts. The company's purchasing managers also review games before they're published to ensure every aspect of the product -- from packaging to content -- toes the line with the retailer's conservative policies.