Is the girl supposed to keep the ring her whole life, or 'trade it in' when there is an engagement?

First of all I have had many girlfriends (what can I say they love the carebear suit) but I guess Im kind of jaded from one relationship i was in. She was the epitomy of material love. She demanded of her one day husband that he buy her everything she ever wanted (she said this meant he had to be rich) and I know this is what people usually do but she finished it by saying that if he didnt get her what she wanted (new clothes car etc.) she would "dump his ***" and she said it stone cold serious and she had to have all three rings plus anniversary rings and all her friends were like this too. So I guess when someone says they better get a promise ring or the whole notion in general just reminds me of this girl and people like her.