We Fly Spitfires has an entry up regarding Global Agenda and its decision to go the digital distribution-only method. I mentioned in my review earlier that it's only available through Steam, but there's also a limited edition version available through purchase on Amazon's US store. Either way it's expected by Global Agenda's developers that if you want to buy it, you're likely going to buy it through Steam.
We've discussed digital distribution here a lot and there's people for and against it on either argument. Personally I'm firmly in the "for" camp– I haven't used a physical CD in years and it's gotten to the point that if I can't buy a PC game online somewhere and get a digital download, I tend to avoid the game entirely. I remember the days of scratched CDs or worn-down CD-R drives making games impossible to install or play and frankly I don't miss it.
But there's also just as many arguments for physical copies as well. Although I tend to keep installation files on an external HD, it's still space that could be lost at a moment's notice if the drive happens to break. It's also a lot of gigabytes to keep on the harddrive itself, usually more than the necessary memory of a similar installation from a CD. I can also think of several times when a digital distribution system has failed to work correctly, leaving me without access to a game I was interested in buying or playing in the first place. In the case of We Fly Spitfires, Gordon ruminates on whether or not the reason why he hasn't picked Global Agenda up yet is because it's not a game he can buy in a store.
Still, I think that the digital method is an evolution we should expect sooner than later. I can't think of a PC release these days that isn't available on Direct2Drive or Steam at the same moment that it comes out in a Gamestop store, and clearly the digital distribution method is advantageous for publishers and developers whether indie or someone like EA. Even with its weaknesses, I think buying and downloading games online is better than the alternative, but not everyone has been as quick to jump on the bandwagon as I've been.