I think that piracy did have some significant impact a couple of years ago, but since Steam and the F2P business model kicked in things have changed for the better against piracy. With this said, however, and to reiterate I do think that piracy did have negative effects a couple of years ago. Also, PC gaming rentals, it died simply because it was obvious almost each rentals ended up being a copied CD-Rom at home and you ended up "owning" the game for the price of a blank rewritable disc.
My local game store used to have PC games for renting, a couple of shelves with brand new PC games, some of them were used though (but not many, most were just new). The only difference was the number of copies and the number of actual games they had. They would have had 8 to 10 copies of Goldeneye 007 for N64 to rent, but they'd have only one copy of Fallout 2 or FreeSpace. If I recall correctly the PC games shelves were emptied almost overnight and the clerk replaced it with PS1 and PS2 (and Dreamcast) games and he basically stopped renting PC games for obvious reasons.
That was back when security on retail PC games disc was minimal to none, back when a mere CD-key was enough for everything to work and all on-line features (when available) would work as well. During those years piracy really was an issue enough so that it did bring an end to PC games rental, at the very least. Then we know the rest of the story, security (DRM) increased, changed... we ended up with on-line features that would work only from "legitimate" keys, and false keys would only make your "offline" (single-player) part of the game work. Today, however, it's quite different. The whole digital download phenomena, the decreasing rental sells (in favor of digital purchases and downloads that is), the F2P model and the "always online" concepts have - I believe - greatly decreased the "incentives to pirate" in general, although it still occurs of course.
Now how much does piracy affect nowadays' PC gaming? Well I don't know, but I do not believe it's as bad as we're lead to believe from what big companies say, they also like to dramatize and I'm not taking their words for truth all the time. But I DO believe that piracy of course still exists, that's a no brainer... but it's certainly no where now as it used to be around 7+ years ago or so.