Right, any earth scientists in the mailing list?
I ran into a geologist friend last night--I didn't get all of the details, but apparently the continents are scientifically defined, in that they are made of a specific kind of rock, and that they are not attached to other land masses in any significant way. So, India has the right rock, but since it's sutured to Asia, is not a continent (although it was until it ran into Asia).
I still kind of like the idea of using the plates, though--gets us the expected continents, but also a "Middle East" and an "Indian sub-continent" all in one go.
Chris