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 man and she 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 men 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 men who are still in the early dating stage can feel extremely jealous as well of course ;)