Originally Posted by J_R_B
You'd have to get a definitive answer from a USTA representative, but I think it's because of the variability of the tournaments compared to league play. In other words, tournament directors can let anyone play any division that they want. League play has very strict rules regarding self-rating and eligibility controlled by a small number of people that can make sure the rules are at least applied uniformly (if not fairly, LOL). In addition, there are no "national" 4.0 tournaments and in general (at least around here), there are far fewer NTRP tournaments than league matches, so it is more difficult to balance the ratings across sections.
J_R_B, I don't think it's possible to get a definitive answer, because there is no definitive strategy in the first place, as evidenced by the fact that each Section can apply their own rules. But I agree with your point about stricter rules and more uniformity in league play as compared to tournaments.
As for balancing the ratings across sections: indeed USTA attempts to do this via national playoffs, and in the end it's possible that 4.0 in SoCal = 4.0 MN - but not due "rebalancing". It's quite obvious that the idea is based on faulty assumptions that a) teams that make it to the playoffs represent an overall level of play in their section, and b) a very small statistical sample (national payoffs) could be extrapolated down to each section and ultimately each player. The former may or may not be true, and the latter is patently bad statistics.