Laptop manufacturers when I bought the C2D did not place emphasis or market my laptop with the number of hours it would last. If I recall correctly the marketing strategy last time was the weight of the laptop, it is the current version where more emphasis is being placed for battery life. It is definitely very unlikely that you would ever achieve the manufacturer's 8 hours because their tests are in a controlled situation and does not account for degradation of parts over time. It is normal for the marketing team to hyperbola something normal to something that is beyond the product could achieve, it is similar to what happened with Bulldozer where the marketing was too aggressive and made the product sounded better than it should be and when the actual product came out it fell flat on the ground.

My C2D is only able to push out 2 hours and there were no marketing to back up saying that it would last 5 hours. Anything that has to do with light will eat up battery no doubt. That is why an eReader with an eInk display would easily outlast a tablet with a conventional backlit panel. 5 hours average battery life is quite good I'd say and more would definitely be better but to have higher capacity we would need bigger batteries and would mean bigger laptops which is not what Intel wants with Ultrabook. The battery life of an Ultrabook would probably be the same with the current notebooks despite the improvement in the processor because the battery has to shrink to fit the slim form factor.