Would it be possible to run Valve's Steam by piggybacking on a Linux app store model? In most flavours of Linux, you have one package manger that can connect to many online software sources (by URL) and is responsible for updates for them as well. It's very tidy, all told, as well as being rather open, because anyone can publish a new software library to incorporate into the model. The only thing Steam is doing differently is credit card payments, DRM and advertising. The DRM just needs to be built into each app, so Steam itself shouldn't be responsible for that, and part of signing up to Steam itself could be a unique URL for your personal purchased software, secured by username and password over HTTPS. The advertising might be a bit more tricky, but if purchases on Steam are handled via the website rather than the client app, then you just do your advertising there. Easy.
Mokalus of Borg
PS - I'm still opposed to the DRM on basic principle.
PPS - And Steam is already available for Windows and Mac OS, so it's only Linux that's waiting.