No one buys a gaming laptop for the battery life - you don't game on battery power in the first place and additionally after a couple of years, the battery becomes a turd anyways.
A lot of the new Haswell gaming laptops are getting over 4 hours of web surfing battery life thanks to Optimus which can shut off the dedicated video card (the only one that doesn't is the Asus G750, but even then, Nvidia's 780m can clock way down to save lots of power). Also the CPU is very power efficient too. So, with the dedicated video card off the laptop doesn't take much more power than a regular laptop.
According to laptopmag's review, the 14" alienware gets about 5 hours in a web surfing test.
In a few years (let's say 4 years) you can always buy a new battery pack for it, probably $50 or less if you shop around.