In retail you measure unaccounted for inventory as 'shrink'. This will be from shoplifting, employee theft, and just plain clerical errors. The average rate is hard outsiders to measure, because a lot of chains don't like to talk about it. Depending on industry and location, the numbers I've seen are in the 1% to 4% of sales range. Which means that for every 50 items a store (thinks they) purchased from suppliers, they only end up recording sales for 49 of them. Different stores record this shrink on their books differently. Some report it as a loss at cost. Which means they just write off the missing items at the price they paid their suppliers for them. Others report it based on retail sale price, which means they write the items based of what they should have been sold for. It all ends up as accountancy magic, and has to do with how you 'value' your inventory. This has a real and measurable impact on their books. In some industries the retail shrink ends up being larger than their profit margins, yet they still remain in business as it is still ultimately profitable for them.
Of course, these retail stores are buying and selling real physical items. Their 'loss' at the end of the year means inventory they can't sell. This occurs because they need to balance their books at the end of the year, and adjust what assets they thought they still had for sale down to what they actually still possess.
Now, typically, save for original media transit disasters or amazingly catastrophic IT blunders, this will be something that never needs to be done in the virtual world. As long as they still retain a copy of their virtual assets, they can continue to offer it for sale endlessly. There is no 'shrink' to write off, because they're already recorded their magic accountancy numbers. Namely, the Cost of acquiring the virtual asset for sale. Which is what it all comes down to in the end. You take the total cost, and you subtract your sales, and your left with profit. In accountancy, there is no magic formula for recording sales you 'wish' you made, or think you 'deserve' to have made.
I'm really tired of hearing about all the 'losses' due to copyright violations. In business, there is only the money you received. You can play marketing and sales games, as you try and measure the size of the market you're in, and the maximum potential sales for your industry, and from how much of the pie you're getting a slice. But this doesn't go on your accounting books.
What's really happening here, is that the media industries are beating their war drums and proclaiming that they're not making the amount of money they think they deserve. You know what I think? I think they amount of money their customers are willing to give them is exactly the amount of money they deserve. And if they don't like it, they should get out of the buggy whip industry.