Jemolk: 3. I absolutely trust myself to follow the recipe, at least with competently written recipes. The problem is that with the Windows Registry, the recipe is frequently difficult to follow because of how deliberately obscured everything is.
Ignoring checking for specific updates for the moment (I can give you the list, as well as how to uninstall them), the commands to disable the update were (run from an administrative prompt)
reg add HKLM\SOFTWARE\Policies\Microsoft\Windows\Gwx /v DisableGwx /t REG_DWORD /d 1 /f
reg add HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate /v DisableOSUpgrade /t REG_DWORD /d 1 /f
Do tell if those are obscure or hard to understand, whether you use the registry editor or the prompt.
Jemolk: It's merely that one of the most fundamental parts of Windows, namely the registry, is extremely badly designed from the standpoint of any end user who has a problem, and this very much extended to removing the "upgrade now" prompts. It doesn't have to be this way, but with Windows, unfortunately it is.
The registry was designed as a centralized place for programs to store information the end user wouldn't need to access during normal use. Unfortunately, developers of windows software tend to think that the old practices are still the best, which does lead to huge amount of issues. When told to use the registry, they just dumped everything there, whether the user should have access to that data or not.
Microsoft does usually document their practices quite thoroughly over at MSDN, but it does take a bit of digging to find the stuff.
Jemolk: I remember complaints of having to install 3rd party software just to get the start button working.
The complaints were "I don't like this modern UI crap. How do I get the old one back", not "the start button isn't working". It's similar to saying "This keyboard doesn't have a numeric keypad, how am I supposed to enter numbers now?". Functionality was there, depending on who you ask better or worse, but some people just wanted the old start menu back. Had a colleague who wouldn't upgrade from Vista to 7 because Vista supported the XP style start menu while 7 didn't. Similar to the Win10 start menu case.
Edit: There was also an issue if you had more than a certain amount of items in the start menu. Can't recall if it was 512 items or 2048, but it was something like that. So yes, you may recall that issue correctly, though I think the number was identified and patched relatively soon (but my memory may be off, off to look for that).
Jemolk: 5. Yup. And it took much less than twice the time to fix the registry than to automate the task.
I can link you a few pages that show what those 3rd party programs do. Let's say a couple of hours reading to understand what they are going to do, then 30 seconds to paste everything on a .bat file and another 30 seconds to run it.
Jemolk: one major reason it's time-consuming is that tinkering with the registry can be dangerous as all hell, and you have to be extremely careful.
Yes. One could say it's similar to modifying the Unix kernel. You need to read quite a bit before starting to mess around with it, but you can mess around, as long as you know what you are doing. Or you trust the one who promises to mess around with it for you.
Jemolk: If it were a simple task to identify the key and make sure that changing it didn't break anything else, and also to make sure that you were in fact changing the right key (it's not always obvious even when you know what the right key is, and I suspect this is by design), then it could be simple to follow step-by-step instructions to deal with it in less than 30 seconds.
Again, for that specific task (preventing Win7 and Win8 to automatically update to Win10) the commands do take less than 30 seconds. Identifying the entries on your own would take quite a bit longer, but that is why there are people who can tell you what to do (provide the recipe) and/or offer their own tools (cook you the food).