When the laptop is in hibernation, it is turned off. So, there should be absolutely nothing wrong with taking out the battery, harddrive, screen, keys, or whatever your heart desires while the computer is in hibernation. The only difference between it and shutting down is that the an image of your programs is saved to your harddrive as it goes into hibernation.
Keane3, I think the posts in your thread that say the computer is not off are incorrectly referring to hibernation, when they are really talking about sleep/standby. The websites they referenced did not differentiate between the two, so they most likely were grouping them together, when they really are different things. Standby is still on, hibernate is off.
So, why would it not be recommended to change the battery while in hibernation? I see it possible, but unlikely.