although this is basically a joke (i have to agree that in every day conversation i'd call the touch a tablet even in its current form - only one that doesn't work), there's some more serious backgound in your question:

tablet as a form factor (leaving open the question of "how low can you go?")
vs.
tablet as a device that's able to perform certain tasks

i tend to think of a tablet as a mini-laptop. i expect it to do everything a normal computer can do. no restrictions dictated by the operating system, by the way you interact with the device etc. ... in short: the one question that defines a tablet for me is "could it run openoffice.org?" (which, of course, doesn't prevent a UI that makes certain tasks easier than OOo on the small screen ...)

so does a capacitive touch screen, a small screen or the fact that it doesn't have a stylus prevent it from running openoffice.org?

in some combinations, most probably. i cannot imagine handling menus that are the size of our current hildon menus on a 3.5"-4.2" capacitive touch screen with my fingers. but i also cannot see a way to have a practically functional openoffice.org without these menus, checkboxes etc. - so, in this case, no, a device with a capacitive touch screen and no stylus wouldn't be a tablet for me once we leave the casual conversation and really talk business. it would be an... appliance.

on the other hand, on a much larger screen (say: 10" or more) with the same resolution it could well work without a stylus, so it could also have a capacitive touch screen.

in the end:
what actually makes a tablet is a specific combination of screen technology and pointing device that allows desktop-like interaction with real desktop-applications. if we can't do that, it's an appliance like any of the 23010764 existing models of portable multimedia-players, game devices, phones or portable DVB-T receivers.