I think something like DLC or microtransactions don't fall under the economic theory that stolen material from otherwise non-buyers doesn't count as lost sales.
Suppose person A buys the game and person B pirates the game. Person A has been shown to be willing to pay for the game, while person B may or may not have bought the game otherwise. In this situation, that theory holds.
Now suppose person A then pirates the DLC costumes or whatever microtransaction nonsense. This is undeniably lost sales, since person A was willing to purchase the game, but unwilling to buy the DLC. Since owning the game is a pre-requisite, they are willingly stealing content that they would have paid for if it came in the original game.
That said, I agree that Viruses is thinking too hard about this NOW, when there are already so many things stacked against him (or anyone for that matter) making any money. Make a game (or a few games), get a handle on your skills, and if you think you've made a game that will earn you money, then start worrying about it. I doubt that the security of your games content is the first thing you need to worry about, or is even required until you have a completed product.