Subscribe to it or not, the concept is that Elin was taking care of the kids and the house and the staff, etc., which freed up Tiger to go make money. In return, she gets some of that money when it all goes bad.
The other concept is that if treat your spouse to a certain lifestyle, then you have some obligation not to suddenly throw them into the street without warning.
One could also argue that stay at home spouses give up their careers and chances at future income, to the benefit of the whole family - they should get something back if they are kicked out.
Finally, if the kids live with the lower earning spouse, that spouse gets a bit of a windfall because the kids' lifestyles are maintained at their accustomed level.
If you don't agree with these approaches then you really need a pre-nup.