I think you know exactly what difference it makes in the world of software development.
Heavily compartmentalised software development with different teams of developers developing different packaged products and all operating independently (since the various Linux packages are all independent projects) with no central management or project management structure is not exactly the recipe for building a coherent desktop operating system that the average non-technical user will find usable.
As they say .... you can't polish a turd, but you can roll it in glitter.
That's exactly the case with Linux desktops. Sure you can make the GUI all fancy pretty.... but if your development style is to wash your hands of what's going on in the backend then you're never going to be able to deliver a final product that's anywhere near as integrated as Windows or OS X.
This is some interesting discussion.
You do remember Windows was born as nothing more than an 'addon' to DOS right?
I wouldn't go as far as to say that linux on the desktop is a 'polished turd'. It has come a very long way in the past few years. - Considering it is free and open source I don't think there is any room for complaint. It is ideal for what the OP is asking for here. You've got a very secure, solid system with free security updates. - The latest version of Ubuntu or Fedora will work with pretty much anything out of the box. You can have just as much trouble getting your old crusty printer or temperamental wifi connection working in windows 8 (and 7!) - It is definitely no more difficult to learn to use than making the transition from Win to OSX for the non teccys. (Or indeed the transition from Win7 to the farse that is Windows 8)
Also, have you heard of Android? - That seems to work alright for just a few non-technical users.
The whole point of Linux is that it's open. We don't want an integrated desktop from the ground up. We want choice. This is why it exists as it does today.