Quick question- when closing iPhoto and System Pref window

[destroyboredom]

This is something I've always noticed but never asked about. How come these programs actually close when you close them using the red x/bubble? For everything else it just closes the window but not the program.

I can understand it for the preferences pane, but why iphoto?

It's not a big deal, more curious than anything.

EDIT: looks like imovie and idvd do it as well.

[mactropy]

In programs like Word, Photoshop or Excel you have the application running an open documents within that app. So, if you click the red dot, it will only close those documents but leave the application open.
For iPhoto you do not have separate document windows and therefore clicking the red dot will result in shutting down the application.