Confused....

Man wins big lotto jackpot - several million - wife from whom he was divorced ten years ago says she is entitled to a share.  And gets one - though apparently not as much as she wanted.  But why?  I've argued this before - why following a divorce should either party have any claim on the other's future assets?  Child maintenance of course is a separate matter - what we're dealing with here is a claim by one spouse for a share in money which the other spouse has come into - by whatever means - after their marriage has ended.  I just don't get it.