I downloaded a torrent of World of Goo as, at the time, there was no demo available for it.
20 minutes later I was paying for and downloading an official copy. Then picked it up again as part of the Humble Indie Bundle.
I purchased a copy of Machinarium after being alerted to its existence by the author complaining about piracy - and after downloading a torrent of the game, first. Got it again with the HIB.
I know that this is anecdotal, I assume I am not typical but find it hard to believe I am unique. More, if there were some magical breakthrough that made DRM perfectly effective and prevented me from doing this, my response would not be to risk purchasing a game where all I know of it is the (paid for) 'review', it would be to not purchase it in those first few weeks but to wait until people I know can provide a report I can trust or to simply not buy at all. In my case, more effective DRM reduces the possibility of sale.
People just rather pirate than buy, if they can
Many, maybe even most, but not all and those who do are not going to turn into customers if you can somehow prevent piracy. Quite the reverse, some of those pirates may become customers.
even if just to keep the piracy out for a little bit during the first few weeks so that people who want to play it buy it because they cant pirate it
Perhaps, but the number of those who when unable to pirate the game pay, rather than wait, is smaller than the total number of pirates and I see very little work trying to quantify that number. More often it is assumed that all piracy represents lost sales.