Again, selling a game early is very different from selling a system at a new price early. When retailers sell games early, it's not a decision that the store has made. It's just some dumb employee who put the game out early because he/she didn't check the street date. Price drops, on the other hand, are a conscious decision made by corporate, and it's not something that an employee can goof up, because it's all tied to the store's database. And it's much more serious than letting a game slip out early. If a store sells a game early, they're still getting money from it. If they cut the price on something too low, they're gonna lose money. Nintendo is still supplying 3DS systems to retails for the MSRP of $250 (the stores buy the systems from Nintendo for slightly less than that, of course, so they can make a profit). If a retailer drops the price to $169.99 before Nintendo sells them the systems at the lower price, they're just going to be losing money.
And, again, don't count on a 3DS Lite or whatever. Nintendo just lost a ton of money, and they'll be losing even more when they start selling the 3DS for a loss, so what makes you think they're going to spend money and resources on a new model? Plus it's been said many times that they designed the 3DS with no revisions in mind. With the 3DS, Nintendo is pushing software updates as opposed to hardware updates.