Why did you decide to have people pay for TESIV DLC when TESIII's DLC was free?
This was because Microsoft has a policy concerning DLC with Xbox Live and requiring the game producer to charge a fee for their DLC. So you can imagine the dilemma, since they wanted to release DLC but had to do it for a price with Microsoft's Xbox Live policy. So they charged for both the PC DLC and Xbox. Here is an exerpt from wikipedia concerning the matter:
Criticism of Microsoft
Microsoft has especially borne the brunt of criticism regarding downloadable content.
Microsoft has since then been known to force developers to release their content at a charge, when the developers would rather release their content for free. Some content has even been withheld from release because the developer refused to charge the amount Microsoft required. Epic Games, a developer known for continual support of their older titles with downloadable maps and updates, believed that releasing downloadable content over the course of a game's lifetime helped increase sales throughout, and had succeeded well with that business-model in the past, but was forced to implement Microsoft's strategy of fee-based downloads when releasing content for their Microsoft-published game, Gears of War.