7
Slicer:
The top page is the index page of the module set as start module. If you choose the News module to be your start module, then the top page equals the index page of the News module. If you choose the Downloads module to be your start module, then the top page equals the index page of the Downloads module.
So what's the difference? The other blocks. Let's say you have the News module as the start module. Let's say you have a custom block to welcome visitors, and assign it to the top page. When a user gets into your site, it's redirected to the top page, i. e., to the index page of the News module, BUT showing the blocks defined for the top page, that is, the custom welcome block. If, on the other hand, the user clicks on the News link in the Main Menu, he'll see the same stories, yes, but he won't see the custom block.
A recommendation? Set your start module to "None". Then create your own top page just by accomodating whatever blocks you want.
Cheers.