If someone pirates something, it isn't necessarily the case that they would have bought it in the first place?
How many times have you wondered what a single sounds like? You download it, if it's good you will end up buying the single or even the album. If you download a movie that has just come out, the same applies, you won't get a good copy, even if you do, in all likelihood you will go and see it on the big screen if it means that much to you. Games are the same, if you like how it plays, buy it.
There are however certain people, obviously quite a few if it's $7bn they've lost, that don't do that, these are the people that wouldn't buy, rent or watch most of the crap that is generated in the first place, so it isn't actually costing anyone any money.
They can go on about lost revenue until they implode, no matter what, there will always be people that don't want to pay for something and will steal it in one way, but at least they aren't stealing it physically from a shop when it's pirated, that really is lost revenue.
<End rant>