Steamworks is architected according to their business model. Prior to Steamworks, if you wanted that kind of functionality (matchmaking, accounts, DRM, etc.) you had to pay $ per unit (whether it be to GameSpy or SecuROM or whomever).
Steamworks pays for itself by bundling the store.
I don't object to Valve doing that. I object to Steam fans who assert that it technically had to be done that way. It didn't have to be that way.
As a greedy capitalist, I am continually impressed with Valve and their execution of Steam. At the same time, I am a lot less impressed with major publishers who don't seem to care about the logical ramifications of what they are doing.
When I make an iPhone game or a game for the Xbox 360, I understand I'm making a title for a closed platform. There are pros and cons to a closed ecosystem. The PC, by contrast, is currently an open ecosystem and there are some tradeoffs to that (hardware compatibility, piracy, vastly different system capabilities, etc.).
If anyone, Steam, Impulse, what have you, were to gain an insurmountable marketshare, then you would, as a practical matter, have to sell your title on that platform and be forced to adhere to whatever standards the platform owner decides to issue.
This isn't theory. It has already happened repeatedly. Next time you lament that games don't come with nice manuals I can tell you precisely why. The largest retailer decided, on their own, what the box size would be on games (and DVDs and music for that matter). Everyone had to follow suit. There isn't some industry consortium on box sizes. One retailer decides what the form factor is based on what is best for them (shelf space). And this leads to all kinds of unintended consequences. It doesn't make the retailer or Steam or what have you "bad". It's not "slagging" to point this out. It is the consequence of market share in a free market.
Consumers are rarely aware of these consequences. But the producers are (or should be).
Major publishers still have the leverage and clout on the PC to make sure that they maintain control of their own experience on their own games. But that won't necessarily always be the case.