Celebrity Working Mothers 2

Celebrity bodies: why do they have to return to pre-pregnancy state as soon as the mother has given birth? Isn't this dangerous.

Angelina jolie is set to star as Lara Croft (the toned warrior) in the up and coming Tomb Raider 3 film. This sparked my interest because a) she is a working mother and b) she is currently pregnant and is said to be planning to start shedding the kilo's soon after the baby's birth. Now I know she has to shed the pounds for this role. But as far as I was aware you can only start exercising gently 6 weeks after birth so you do not injure yourself. Yet many celebrities 'have to' lose this weight for these roles. This begs the question how dangerous is vigorously training a post-pregnancy body??