I think part of the issue here is that as astronomical observation tools improve, science is going to discover more and more large bodies that may be considered "planets" under the (fairly loose) existing definition, and they needed to nail down what was "officially" considered a planet. Either narrow it down to 8 of the current planets, or include an additional 3... and possibly a lot more!
After all - if the current 9 were tough to memorize in order, how are the next several generations gonna remember 12, 15, 20, or 37 planets?!