It all depends on where you look at. I can't remember the last corporate software piece I saw being delivered as a desktop application.

Stand-alone software for iOS has one advantage over web applications in that users sometimes face lack of connectivity. The Facebook app, IIRC, is delivered as a standalone app, but, in reality, is nothing but a web application. It's not alone and there are definite advantages to their approach. Most software appears to be entertainment - games, social thingies etc. They are the kind of games one would expect to be delivered as a Flash application within a brorser on a desktop.

I am not familiar enough with the Mac App Store, but, while there are some more "serious" offerings, in line with the desktop apps I mentioned, most of them appear to be, again, games and other entertainment related stuff. That and front-ends to net-centric applications such as Evernote.