It sounds to me like Apple is handling this very well. Obviously there was a mistake on their website after the keynote, but it was mentioned in the keynote itself and on the actual product page on Apple.com that ONLY the 2.4Ghz model would have the backlit keyboard. I really think there are a lot of people here that knew this, and ordered the lower model anyway hoping they could complain their way into the better model for free (not accusing the OP).
I would of done that.
Teach Apple that careless mistakes are not acceptable.