When you are married, have children or own a house together, you tend to depend a bit more on your partner's choices.
If you are a woman and he decides to run off with someone else, it is not only your emotional security which is threatened, it is as well your material well being.
This is why women who are in this type of committed relationship (with a common "base") might feel slightly more prone to jealousy than those who are "only" dating.
Now that's only a very slight tendency.
Many women who are still in the early dating stage can feel extremely jealous as well of course ;)