Perhaps the existence of some productivity apps (most with limited functionality) such as Pages, Numbers, Documents To Go, etc. has led folks to expect the iPad to be a fully functional computer. I don't think Apple shares that view. If they did, they would have used OSX rather than iOS as an operating system.
Giving it a file system would still not make the iPad a fully functioning computer. Due to the limited power source and great battery life iOS was an excellent choice for the iPad. It just needs a way to store user docs to make it a more complete and independent piece of hardware. This IS the problem as Apple wants it shackled to iTunes!