Alot of windows software can work by copying folders around. I have software running on windows 7 that I haven't installed since I ran MSDOS (circa 1994).
Microsoft even promote it, it's called xcopy deployment.
http://msdn.microsoft.com/en-us/library/aa302347.aspx
For the apps that don't work like that you can often get portable versions
http://portableapps.com/
Let's not forget that their are apps on the Amiga that require installation, including copying files all over your boot partition. So it's not an operating system, it's down to the applications. Software these days is mainstream business, the bigger the business the lower the quality ( and that holds for more than just software ).
I don't think we can get the whole world to rely on software that was written 17 years ago though. A friend of mine is having trouble getting his iphone to sync now he's on ios4, itunes is a particularly hopeless piece of software. I doubt he's going to have much more luck trying to sync to an A500 though.
LOL. I think he'll have to try the 500, it works always best.
Yes there is a lot of software that does not touch the system in any way in windows.
I wrote it was a temp dir from the old Amiga500. The point was that i never needed to reformat and reinstall the entire system and applications. There are certain files and folders it's wise to have an extra copy of on the Amiga of course.