Ok, can we just forget file systems for a second. The file system serves a purpose, file management. I want an easy way to search, sift, and or browse through the files on any device I have. If that requires a file system, that's fine with me. If Apple can do it without one, that's ok too.
I don't use a Mac, so I have no idea what OS X does, and given that even Apple has admitted that they lost the PC wars, I'd say that saying that we should follow their lead in that regard is a bit of a joke anyways.
Though, I really do like iOS. My problem is the same as someone else has stated. I've got different versions of files in all sorts of apps and no way to consolidate and search, sift, and/or browse through them. If you do any real word processing, this will be a major issue for you because Apple's solution so far just doesn't work. If you're fine with what they have, that's ok too...
I think the real reason that they're shying away from it is the whole sandbox approach. No app really touches another app or the OS itself. That provides a lot of protection from viruses, etc. They open up a common space, and who knows what could happen...
This isn't about trying to be PC or Post-PC... Though, given the iPad is a Personal Computing device which just happens to be what PC stands for, and the fact that so many people love to use the iPad to say that Apple is now the largest PC manufacturer... I don't know. I have a hard time buying that statement. Like everything else with Apple, the price is just a little too high for me.
Just my two cents.