Its a multiplatform era with development aimed primarily on consoles (because they sell the best). Its the same with consoles, pretty much any 3rd party developer has there game on every platform, only the 1st parties really create exclusive titles (the PC doesnt have first party devs, nature of the platform).
Although this could change if the PC hardware makers put together some dev teams to create the games (i think Intel actually have a game being made). Also -
Crysis has sold at least 1.5 million from the last time they mentioned sales (which was quite awhile ago).
BioShock has sold at least 1 million on the PC.
STALKER SoC has sold 2 million copies.
CoD MW sold nearly half a million in the first month of NPD sales, which is America only, without digital distribution included.
World of Warcraft has recently been announced that it has sold 8 million copies in the US retail alone.
The Witcher has sold 1 million at least.
Sins of a Solar Empire, which had a small budget (compared to todays standards) and nearly no advertising, was originally only released in US retail with DD available, has sold at least half a million.
PC games can sell, and they can sell well. Sure the figures aint up there with console figures, but thats always been like that right ? Games have always sold truckloads on consoles due to it being a mainstream accessible platform, which have huge marketing teams behind them getting them known out there.
People also need to stop lumping the consoles together. Look at the PS3 and Killzone 2. An exclusive triple A FPS with lots of marketing, has sold, from the last reported figure, 1 million. Compare it to Crysis and you have something similar.
Most people see sales of things like Halo and Gears as the uber sales successes (which they really are), but think anything that doesnt reach that as failures, which is ridiculous.
Blah i think im loosing track here, anyway the end

.