Purchasing my copy as soon as I get home. $20 is, in my opinion, a nice middle-low for a game (considering that the cheap ones are $5-$10 and the hyped ones around $60) and every indie developer deserves support if their prices are reasonable and you enjoy the game at all. That said, I will then probably download the game from the BitTorrent anyway, just to avoid the slowness and hassle of Steam. So I guess I will not affect the balance either way.
But, unfortunately, unless they reveal exactly how they're measuring the ratio, the 90% is just empty words with no weight. I wish we lived in a world where you could believe what developers and publishers say about piracy, unfortunately thanks to a lot of companies pulling huge and supposed-to-be-shocking numbers out of thin air blowing the problem out of proportion, we don't. So I don't see any reason to believe this is anything more than an overreaction to seeing a lot of people sharing on BitTorrent.
EDIT: Never mind, found their blog post. Technique seems reasonable. Though it begs the question, without leaking to the torrents, how many of those 90% only found out about the game from torrents, and how many would have purchased it without free download option. Because unless they would have (discovered and purchased), they are not lost sales, they're free advertising.