Why does traffic from the WAN port HAVE to also show on the LAN port?

Take this scenario, which is a dumbed down version of what I'm looking for.

Main site
Remote site 1
Remote site 2
Remote site 3

If remote site 3 needs to get to main site, and it is not directly connected, then it must route through site 2 or site 1 to get to main site. So, if site 3 is routing through site 2 to get to main site, why would you see traffic on the LAN port of site 2? You'd only see that traffic on site 2's WAN port... correct?

The router does have a management console. There is every freaking option you can think of in there... except to show active connections. This is a motorola vanguard router. There are no books out there on vanguard routers. The manuals SUCK!

I can't wait till I'm working with Ciscos... I hate motorola with a passion.

I understanding what you are saying about listening to traffic on the outside of the CSU.
I kind of figured it'd be pointless... but I wasn't sure.