As for the keyboard, you'd eliminate ALL tablets from this debate with that clause, regardless of the OS or hardware capabilities. You'd equally have to include any iPad or other mobile device used with a BT keyboard or docking station. This is a condition that introduces variables not able to be tracked easily, and based on user preference not device capabilities. Simply by including a cheap $20 keyboard in the box, apple could essentially add every iPad as a mobile PC legitimately.
No PC is required for an iPad at all. It supports on-device activation and thus does not "require" iTunes at all. The only connection to a PC that is required it for syncing an existing media collection. However, this step can be bypassed by adding a mobile.me account and storing music and other files in the cloud (including being able to play them in the background). Files can easily be moved in and out through mobile.me or drop-box or any other similar service.
Removable storage requirements can also equally be countered through use of the cloud, drop box, and other services, and in fact, many NetBooks and even some laptops do not include a removable storage option. The iPad further DOES support SD as well as camera connection, and that can in some ways be equally used as storage. Again, this is a use case or personal preference aspect. The medium used is not determinate of the function, so long as the device can in fact create, open, edit, and share information, it meets all of the requirements of a personal computing device.
You say it requires USB, i say USB is a security risk ( to virus, data loss, and theft) and the cloud is not only more convenient, but safer. The odds of you needing to transfer data to someone else's mobile computer or any other computer in such a case as an ad-hock wifi connection can not equally be made, or connecting it via a cable, or running an app to share a file (even devoid of 3G or WiFi service offerings), will be highly rare and thus anomalous. It does not have to work in the middle of a desert to be considered a computer, that is a specialized use case, and additional equipment requirements may apply.