If I google and download a .deb package, sure it piss easy to install. I double click it and software centre opens and acts like windows' install shield. Its the same user experience as installing an .exe or a .msi... sure.
However, not everything comes as a .deb does it? If it did, we wouldn't be discussing this as there would be nothing in it.
The fact is you may need to uncompressed things, manually make directories as root, chmod, chown stuff using terminals, run shell scripts, add repositories etc etc. I would go on but you've got my point by now. Hell, vmware made up its own extension .bundle
I'm a technical user and an confident saying although I can pretty much install anything I need, there is no structure or commonality between app installs like there is in windows. Every app installs or installs exactly the same. All the files are in the same places. With linux this simply isn't true.
I am the technical lead for desktop support in my company so I spend a lot of time working with both engineers and administrators alike, across both platforms. Everything is easier on windows. Teaching the use, supporting or fixing issues... all easier on windows.
Do I love Linux? Yes! Would I recommend it to my mum? Pfft no chance.