There is literally nothing that Jeter has on A-Rod in the postseason outside of batting average, and since A-Rod's got him by 12 points of OBP and 34 points of SLG, the average advantage is moot.
This is seriously a statement that only a person who doesn't really watch baseball could make. You're basing it solely on numbers. You can punch numbers into a computer, and it could tell you A-Rod's not that bad in the postseason, but anyone who actually watches baseball knows the situation is a little different. Outside of the 2004 ALDS against the Twins and his magnificent 2009 playoff run, A-Rod has failed in almost every, single big spot he was put into. Anyone who watches the games knows this. And it's not like, "Oh, man, A-Rod really hit the ball on the screws 4 times tonight. Bad luck." No, the man has had entire series where he looks absolutely lost at the plate, swung at everything, and if he didn't miss it, either popped up or hit weak dribblers.
At the end of the day, I'll take the championship he carried the Yankees to. If he keeps being a playoff dud, it's fine. But don't ever try to act like the difference between Jeter and A-Rod is negligible, because it's not. A-Rod has all of the physical talent in the universe (well, at least, he did), but Jeter simply finds a way to will himself into succeeding in big spots.