Now, that last one in your list above is the one many people fall foul of. So many times I get home and my wife says she has been trying to perform a task and hasn't been able to work it out, downloading and installing all sorts of image viewers/resizers, PDF makers etc from random places... which is where most of the junk comes from.
As for locking a computer down, in a business environment that is the norm for non creatives. Business users really don't need to be able to surf unknown sites, download and install software etc... so for them a laptop with office installed and then locked down is a perfect solution. And if for any reason it did go wrong you utilise the fact all laptops purchased are identical and share a common backup image, so they just get wiped and the fresh image written, then you just setup the logins and hand it back. Simple.
Not so easy for home users whom do what a bit of freedom to so what they wish. My wife being a teacher needs some freedom to do things with her laptop dew to work requirements, such as for example researching stop frame animation software. And that is where the junk enters.
One mad thing in her last school though were the iPads they purchased for the school to use. These were locked down and only had the default software installed. I've never owned an iPad and use Android tablets, so was shocked when I was playing around with one of them and discovered how little the default setup can do without installing apps. Contrast that with Android, and in 4.4 you can get away with doing most things without the need to install any additional apps.
And I agree, as well. I'm really glad that there's now something we can all point newcomers to the field to, which is, I think we'd all agree, a damn sight safer to use. I never liked it when people asked me for advice on picking up a computer, say, fifteen-odd years ago, as it was always fraught with such issues...