Precursors is $9 (check it out!), and so is Xenus II White Gold (the sorta-sequel to Boiling Point, maybe check it out!).
That's not always the case. I've been able to download Bad Company 2 from Amazon, where I bought it, and from Origin, where it also registers, for example. But one steadfast rule in the world of downloadable games is that they're all digital, meaning that we don't need to waste e-ink with redundant "digital"s.
Edit: I should probably throw in another recommendation for Just Cause 2, for anyone still on the fence. $5 is a bargain! But please note that it will not run on Windows XP. You require Vista or 7.
I purchased a copy of Precursors and Xenus II White Gold after reading about them on neogaf. Haven't got a chance to play them yet though. Anybody who has mild interest should look up that thread.