From the FAQs:
Is this the Valve console? We think of Steam Machine as an extension of PC gaming, not as a console. The traditional console model is to sell hardware at a loss and make up the revenue with subscription services or by selling games that are locked-in to the hardware. We think this can make sense for a single business in the short term but that open ecosystems are better for customers over the long term. PC gaming's history proves this: The openness of the PC gaming space has enabled it to be the primary driver of hardware and software innovation for decades. The strength of PC gaming is the ability to play the games you want on the hardware you want. Steam Machine is a solution to these problems (and we think it's a great one), but it's not the only solution, and we don't want it to be.