First of all, if 300,000 copies were torrented, they cannot say that those are lost sales. Because for all they know those people could never afford to pay $60 for that game. So, applying statistics to bogus numbers doesn't really help the argument one way or another.
More to the point on your original question: torrent websites will not kill PC gaming. If you're familiar with the said websites, you should already know there's just as many cracked/copied versions of console games you can download. So, unfortunately for developers, piracy applies to consoles too (but publisher companies don't want you to know that).
Besides that, torrent sites are not the problem, because no torrent website charges people for the downloaded games (none that I've heard of). So, even though torrent websites are illegal a developer/publisher cannot claim income loss since no income was incurred by the said torrent site. However, there's a pretty large spread "black market" for pirated games on the street. This is especially true for countries in for example eastern europe. There, pirated game retails for about $5. That is the true income the publisher lost, because people were willing to pay for the game, except they paid for a "discounted" game. That's a lost sale, and that is the biggest problem that exists in the piracy scene.
Torrent websites contribute to the spread of pirated copies, and make it easier for those back alley vendors to make a quick buck since all they have to pay for is a CD+burner to possibly make loads of money at close to 100% profit margin.
And again, don't kid yourself that this only applies to PC gaming. The situation is exactly the same for consoles. The only reason we are seeing games consistently developed for consoles instead of PC is console hardware has stayed the same for 8 years. Every developer and their grandmother has developed libraries and engines for console coding, so only thing they got to change is put in new game content. For a PC every time you make a new game you got to update the engine to keep up with new hardware/drivers/APIs/etc. It's much more costly to develop for PC, and with industry tendency on making a quick buck for as cheap as possible, consoles is an obvious go-to platform.
As an off-topic: companies like EA will ruin gaming in general.