Apple is always a bit dodgy in their specified battery life. Leaving the iPod on shuffle, or having it play all the songs in order will result in a 12 hour battery life because of the way it manages power, but if you played around with the controls 'X' number of times on a 3G iPod , and got 6 hours of battery life, and played around with the controls 'X' number of times on a 4G iPod, it'll only give you a small increase in life, not 4 hours.
The reason I say that the battery life will be extended "slightly," even if you were to still play around with the controls 'X' number of times, is because it now uses a click wheel instead of the touch wheel. The OLD iPods had 10 hour battery life, and that was BEFORE the touch wheel came out. With a touch sensitive wheel, the iPod was sensing for an input continuously so that once you touch the wheel, it responds immediately. With the click wheel, the iPod doesn't continuously sense for an input. It knows when it receives an input when you physically click down on the wheel.
So the click wheel is the only thing that really makes a difference if you like to fidget with which songs are played, and will probably give another 2 hours of battery life or so. Don't know yet.