Of course, this quote doesn't include things like promotional images for games. It's a store, so it will promote its products. This is referring to like, Doritos. In response to Microsoft Xbox and Sony PlayStation integrating ads in their service, Valve said that it doesn't make sense for Steam. It might make some short-term money, but it doesn't bring value to the user, it could harm the long-term relationship with the user, and it probably doesn't even sell Doritos.
Doesn't go with Mountain Dew.
In my opinion, it doesn't really matter. An ad-free Steam is nice, but I don't feel it would that it would affect me much as a user (although that would need to be actually measured to be a valid data point). I also think that its lack of effect is a fallacy. When surveyed, the vast majority of people believe that advertisements don't work on them, or just let them know that products exist. They're wrong.
I do believe that it would affect their long term brand perception with customers in general, though. Several brands have tried to get involved in gaming platforms and events, and the inevitable ads and product placement get ridiculed. It makes sense that Valve would avoid that, especially since their brand is what's keeping them on par with their competitors.
What do you think, though? Do you believe that you would mind? Or would you just shrug and ignore them (unless they're obnoxious)?