I have to say that Angry Birds on a 27 inch screen is a bit overwhelming.
The Mac App Store has a few idiosyncrasies, but it's a pretty good start. Instant gratification, or slightly delayed gratification with my connection, has always been a good retail model.
@Modred189, Steam only sells games, as far as I know. This store sells everything, provided Apple will approve it. There are definitely some very useful apps that will not gain approval under Apple's current policies. Fortunately, unlike the iOS App store, it is not an exclusive store. There is even a competing store called Bodega. It's been around for a while but never really caught on, mostly because it's never had very many apps.
And when did we become so mobile centric that we call everything an app? Computers used to run software and programs, and occasionally applications.