I'm currently studying ISCW and have been reading the official exam guide. In chapter 5, it talks about the setup of NAT, DHCP then config a default route for the SOHO network.
I have an older 2611 router running at home with NAT and DHCP. It is being used to separate my kids network from my own network to implement a time-range blocks to prevent them from spending too much time on the internet.
I remember when I set it up, I didn't put a default route. I went back to my 2611 config today and surely there is no such thing as "ip route 0.0.0.0 0.0.0.0 interface ethernet 0/0". However, show ip route lists a default route as "S*" points to the next hop route to get to the internet.
So, it seems to me that NAT installed this route on the route automatically (and things are working perfectly). If this is the case, why the book (page 119) says to config a static default route on the router??? I have no routing protocol running on this router.