buyers of the Samsung GALAXY Nexus are given a 2000mAh extended power cell and a bigger back cover to accommodate the bigger cell. That goes with the 1750mAh battery that is standard with the device to make sure that your Samsung GALAXY Nexus serves up Ice Cream Sandwich all day without needing a charge.
It looks like a good sales strategy by Samsung that really would be appreciated in the States where the Apple iPhone 4S and the Motorola DROID RAZR have both launched without a removable battery. But for now, it would appear that Samsung is just giving some extra loving to those living in its backyard.
source: Naver (translated), Reddit via Phandroid
A 2000mAh battery is given free to South Korean buyers of the Samsung GALAXY Nexus (L), compare its size with the Samsung Galaxy S II