Primarily as there's a very slim chance you'll find something that has Firewire but not Ethernet. Except the Apple iPod - hardly a target market for DSL I guess :)

I know very little about old Mac networking. I did get my Duo 230 net-connected (running 7.5) I think that was through Open Transport. Guess it wouldn't be abad idea just do a search on Open Transport to see what buttons folks need to press to do stuff like DHCP, etc.