I think the usage paradigm of not accessible filesystem is wrong. And this doesn't change with jailbreak. You may have access to files then, but it doesn't change the workflow. The N900 still has the classic computer workflow (the N9 doesn't, in spite of the access to filesystem). Get a file (e-mail, bluetooth, usb mass storage, sd, download or whatever) , edit it with various applications, transfer it wherever you want (again, sd, usb, e-mail, upload etc.)

Any device that does not support this workflow natively, without workarounds, for me is not a computer.