well thats just for advanced stuff that might not work for the type of connection. also has to do with other factors and your ISPs network contrbutes to alot of the static routing issues sicne they decide thier backbones pretty much.
and also routers have solved lots of problems and what if wireless were to come into play. routers make it eaiser to expand your networks!
yeah and it also stops the packets that go to your external ip adress like worms and stuff no way for them to know your internal and its great *echo*:S