Security behind a router?

[Gary Fritz]

I just installed VNC on several systems and, remarkably, it 
worked quite well with almost no twiddling.

I changed the AuthHosts value to permit only hosts on my local 
LAN to connect.  (I.e. set it to "-:+192.168".)  I assume this 
will prevent ALL connections from any outside hosts.

Question:  All hosts on the LAN are behind a router.  In this 
case, is it necessary to go through the pain of setting up SSH?  
Or can I safely assume that all traffic between server & clients 
will stay behind the router, so there's no way an unfriendly 
could snoop them?

Gary