Ash_735 is correct, piracy is a massive problem on PC, and in many ways the gamers who actively participate in it are the people responsible for the platform's sudden and sharp decline in popularity with developers.
However, the answer does not appear to be software like SecuROM. As has been seen with countless other software products, the pirates always find a way around it and in many cases it ends up being easier to install the pirated software than the real thing. Software like SecuROM and Windows Genuine Advantage serves only to punish legitimate users because they are the only people that ever see it - the pirates don't!
I think it will only be a matter of time before we start seeing some AAA titles being distributed solely online via services like Steam (which are much better at preventing piracy than any product like SecuROM). When this day comes (it can't be too long now) then the piracy movement on PC will decline sharply.