You sure about that?
We can define a plate as anything that moves relative to another plate after all...
The fact is simple plate tectonics does not really apply within continental landmasses, particularly those made up of a carnage of collision zones such as we see in the Middle East, and South Asia.
We can no more rely on a tectonic definition of the continents than we can on a political one. We must simply accept that they are defined... as they are defined. It is of course obvious that the Europe/Asia divide is as much to do with cultural differences (as perceived by classical Greeks and medieval Christendom) as much as physical geography.