From what I remember, people originally got on Steam because that's how you got Half-Life 2, which the world was clamoring for. They put up with the problems until it got better because Steam was how you played CS and HL.

As for the DRM... has it ever really been onerous? The only case I think of is if you don't always have access to an internet connection, and they have workarounds for that, though they admittedly are imperfect.

True, the hypothetical/potential failure modes suck - being locked out of your account and losing your games; Valve goes out of business and you lose your games; you're offline and can't switch to offline mode and thus can't play your games until you find an internet connection. That said, I've always been of the impression that most people don't mind Steam's DRM that much because doesn't stop them from doing what they generally expect to be able to do and want to do with their PC games, which is sit down at any PC where they can log in on Steam and play them. This is unlike DRMed music and movie files: sure, DRM prevents you from making unlimited free copies for your friends, which I think most anyone would agree is reasonable, but it also can prevent you from doing things like changing formats or resolutions or storing/viewing from certain devices.