I agree. $400 is really not a fair deal for the customer... It might be their cost, but no one on our end would ever be able get that feature for that price on any make or model.
Unfortunately, they seem to be doing this to get people to upgrade to the Summit Reserve package to get what they advertised as a standard feature for Overland and up. I think Overlands have it, but you also loose some of the nice interior options. As for adding an eLSD later, it is probably impossible. Even if it is possible, it will undoubtedly cost more than upgrading to the Summit Reserve up front since it requires an entirely different rear axle, and likely ties into the onboard computer.