Honestly, this is a lot bigger than just drivers and linux distros. Steam could enter a much larger market - even larger than the one it has now - with this. Consider the following:
It's no secret that Valve was planning a sort of home entertainment system aka Steambox. We all saw the articles, it's easily searchable via google. When it comes to E3 (well, it used to), we all look towards what each major player is looking to throw down on the table - their console exclusives. In a market that's quickly becoming more and more focused around multiplat games, we have a fine-tuned linux distro that Valve is promoting for living room entertainment systems. They're also talking about media integration and streaming as well for SteamOS. When it comes to consoles and PCs, it's also no big secret that people like to brag about their console/PC of choice being superior on internet boards ad nauseum.
Here's where it gets really good. Lots of console "exclusives" end up coming to the PC anyway as ports (despite the quality of each port varying) and the PC has its own market. If you look around, there's a lot of movement into small/form-factor PCs. Even Apple has their own version of it. We've seen pictures of the Steambox - it's supposedly pretty damn tiny. Loading SteamOS onto that thing is going to provide the features necessary for media playback and gameplay. This has the potential to seriously blur the line between the PC market and the console market and create some very interesting consequences. It gets even better after that, too: the theorycrafting can get really good if the customization thing about the Steambox comes true. To quote a friend of mine,
1:44 PM - Harrs: this is a scary new world we're living in
1:44 PM - greatstalin: i love it
1:44 PM - Harrs: oh fuck yeah it's awesome