Why Are Notebook Battery Figures So Misleading?

From Hot Hardware -

AMD's senior vice president and chief marketing officer Nigel Dessau has a insightful blog post on the state of notebook battery figures. Currently, manufacturers just provide a single figure regarding battery life, usually generated by MobileMark 2007. Unfortunately that number is usually a best case scenario instead of real usage. (MobileMark 2007 generates a rating of battery life when the PC is running on average less than 5% utilized, or as he calls it, "fundamentally idle." Or in other words, it is not really being used.)

E.g. Asus claims its Eee PC 1000HE can get 9.5 hours of battery life. But is that with the WiFi on all the time? And is the brightness set to full as well? Yet when reviewers get even just 6.5 hours, they are happy. Would we react the same way if a car achieves only half of its advertised city MPG consumption?