Why some games appear in App menu and some don't?

[Turin Turambar]

For example, I have downloaded Engima with Synaptic and it automatically included the game in the Application/games list.

Not so with Supertux, although I have downloaded it with Synaptic as well.
What's the catch?

ThankS!

[Burgundavia]

Some games do not appear on the menu as they are missing a .desktop file, which is tells gnome where the app should be.

Corey