If I understood you correctly, your suggestion is that desktop software should be hard to find, it should be installed from whatever website I happen to ultimately find and it shouldn't automatically get security update
So innovate dude. Create a stable API that developers can hook into so their applications can update themselves without re-inventing the wheel. Neither OSX nor Windows really provide a good way to do this, which is why every self-important installer puts in their own auto-update mechanism.
The idea of a central repository is one of those ideas that sound logical in theory, but in practice it simply will not scale at all. It might work okay for the iPhone which has a limited use or the current generation of linux distros who have a fairly small set of software available, but it will never work for a mainstream operating system that is expected to run *every* bit of software in existence.
Will Quicken be in your repository? TurboTax? SimCity? World of Warcraft? The software for my old TI-89 calculator? The software that came with my UPS? What about DB2--all the versions with all the varying patches? What about the specialized medical imaging software used by my doctor? What about the software used by the CNC Mill down at the local foundry? What about the POS software running at the pizza shop down the street? What about the software for my Harmony Advanced Remote? Will these be in your repository? If they aren't, how do you propose I install them?
Sorry, the idea of a central repository for every single bit of software a computer might run is, well, insane. Who maintains it? What happens when it goes down by mistake? In fact, it sounds a little cloud-like don't you think? Are you folk supposed to be anti-cloud?
So please tell me where I will be going to install the software for my old Harmony Advanced Remote?