Wow it took a whopping 52 posts and on to page 3 of comments for the first fan post to appear.1. They always sell it as "up to" x hours of battery life. You're not guaranteed the number they say.
2. From the sounds of it it appears that whatever they had been using to calculate time remaining on the battery couldn't keep up with the processes in the computer, especially if the load is constantly changing.
That must be a new record.
I didn't think I was going to find any fan posts in this thread, oh well, I'll admit i was wrong