Well, on Debian potato (or woody), dhclient is right there, as a package to install in dselect. It's interesting the way dhclient works in handling cross-platform issues. The binary itself does only platform independent things. Most of the platform specific implementation stuff is in /etc/dhclient-script, which is customized for your platform.
In that file, route is definitely called (correctly, as far as I can tell).
Debian also supports pump, but I'm not sure if it sets the default route correctly like dhclient seems to.
Thanks for your quick reply,