Today, for my comps, I read some of Jacob Neusner's Introduction to Rabbinic Literature. Neusner, like Martin Jaffee (I think), says that rabbinic literature moved from a focus on temple to emphasizing the sanctity of all Israelites. That was why they focused on table purity. The question would then be, When did this development take place? After the destruction of the temple? But the Gospels present those sorts of concerns existing before 70 C.E. But people can always say that was an anachronism.
I somewhat disagree with Jaffee when he says that rabbinic literature differs from the Torah in that the latter is concerned primarily with sanctuary purity. That's true, but people had to wash and be pure away from the sanctuary. But Jacob Milgrom suggests that's because the impurity could travel to the tabernacle, almost like defilement floats. If the rabbis thought the purity of the Israelites was the important thing, though, that would explain why more observant Jews today--even in America--are concerned about defilement from a corpse. At least I heard something to that effect at Jewish Theological Seminary.
Sorry that I'm not too precise today in my documentation. I have somewhere to go tonight. When I get home, I'll watch Smallville. I have missed who knows how many episodes of the new season!