In practice, if you forget about system files and such, I'd estimate 9 out of 10 people have all their documents in a single flat folder, which they only access through their word processor or whatever they use to open them. They have all their pictures and video in a tool that organizes them into albums and such without them having to deal with folders. They have all their music in a program that keeps them in a library somewhere, which they never manipulate on the file system level. And so on. Or (also very common) they just dump everything they touch on their computer on the desktop. This is not because making folders is 'too complex', but because users can't be bothered to come up with hierarchies to order where there files are 'stored on the file system' or whatever, they just want to make their changes persistent and be able to quickly find their files later.
For the vast majority of people, folders are an anochronism. It's not that they are 'hard' or 'complex', but they are simply not essential, and actually quite limiting for file management. The whole idea that the artefacts you create or consume are best structured as a tree really doesn't make a whole lot of sense. Especially not if you want to have all your data available on multiple machines which may have wildly different file systems such as desktops and mobile devices.
This doesn't mean we should all have big piles of files with no ways of structuring them, but it doesn't mean folders are the epitome of file management either. A database-like file system with powerful search options could definitely be much better. From an end-user perspective, organizing files by the applications they can open them also seems to be a pretty good idea to me. Attaching metadata and tags to files so you don't have to superimpose them using a tree-like structure would be a huge improvement.
I'm not saying that what Apple is trying with iOS and now OS X is so great we should all hail it as the future of file management, but personally I think they are moving in the right direction. Ideally, end-users should be able to operate their devices and get to their files without even knowing it has something as abstract as a 'file system'. Just sit down, get the file you want using whatever criterium makes the most sense for finding it, manipulate it, and have the same file available on every other machine. I think this is the vision Apple has, but it will take lots of time to get there.
Also, people mailing files to themselves to get them on their iOS devices literally has nothing to do with how the iOS file system works. Folders or no folders would not make any difference.