It's unfortunate L4D2 and DA:O are two of few titles that were actually good and sold well. Except the two of them there was MW2, which was like the no1 seller on steam till the end of January when ME2 and BC2 beta preorder became available on steam, even through the steam holidays.
Borderlands I do not think sold well on the PC, I think it had to do with it being a console port, the securom and lack of mod tools. When they announced that they hit 1 million multiplatform and I do like you did checking the VGchartz, subtract the console sales from the 1million the PC version would seem low.
Torchlight was good but mostly pirated for what I know. Sim 3 sold a lot.
I think what saved PC gaming (maybe saved is not the right word, but refering to the 205% growth of steam) last year was tremendous growth of Indie game developers and Valve surely did a good job on helping them bring their games over to steam and the steam holiday sales were just ridiculous.