I don't think a discussion of this sort can be carried on coherently without an agreement on terms. What do the orig. writer and subsequent posters mean by "potential?" As has been pointed out, are we talking about aging, or price obtained on the market (which is how the orig. Bordeaux classifications of 1855 were derived), or just ineffable "goodness" or what?
That said, I agree with Al: The omission of Pinot Noir, however one defines one's terms, is either accident or idiocy. And Zin, however satisfying and useful a wine it can be, simply does not achieve, at the high end, what these other varietals do. (At the low and middle ends of the spectrum of course, a good zin can certainly hold it's own against a good chianti, et. al.)
Finally, I have not tasted the very greatest examples of either burgundy or tempranillo, but none of the termpranillo I have experienced gets anywhere near the B+ - A- burgundies I have had. I have enjoyed many Spanish wines, principally Riojas, but have yet to experience transcendence in a Spanish wine as I have in Barolo, Chianti, Burgundy, Rhone and Bordeaux.
"Strange how potent cheap music is."