When I think about how Valve built their brand, at least in my eyes, it was a two-step process. First, make a few great games (and no high-profile duds). That's your foundation. Then add all the Steam stuff, and be careful to never ever screw me over. EA isn't good enough at step 1, and while they haven't screwed ME over, there are too many people crying and screaming for me to ignore it.
Who else could diversify the digital-distro ecosystem? Maybe Blizzard? Except now it's Blizzard/Activision, and Activision seems sketchy this era.
Maybe ZeniMax? (I dunno what Zenimax is like as a corporate overlord, but if you sum up the brand credibility of all their subsidiaries, that's a lot of credibility! I might not enjoy playing id games any more, but I respect the hell out of them, and open-sourcing all your engines is exactly the kind of trust-builder that an overlord needs.)
I buy from steam because I don't have to deal with any of this bullshit. It's stress free and easy to use. It's the same reason I buy from iTunes. The only computer game I bought that was not on Steam was Starcraft 2. And that was mostly because of nostalgia and great reviews.
The sales, prices, and income mean I buy more games. When I spend $60 on a game it's an investment. I want more than $60 worth of entertainment from it, otherwise I'll just take the g/f to the movies or on a date. When I spend < $20 on a game, it's on the level of a lunch. If it can last a few hours I'm happy.