I realise this is very similar to the way MacOS has worked for ages. It is in stark contrast to the way Windows works and even the way Linux works. Though, I don't see why an RPM/DEB installer app couldn't be made just as simple (or simpler). Integrated into Nautilus and Konqurer etc.
Don't most distros let you click on a .deb or .rpm and have it popup a dialog asking for the root password, telling you it's going to install it? I think debian can also go off and grab any dependancies that the deb might require from whatever media you want. Part of it is that applications aren't "documents", and people often think of files == documents. Thus people don't often seem to realise that applications actually exist in the filesystem. (Speaking to people in the Windows/Linux world anyway).