Sarge still gives you the option also. Exim 4 is installed by default.
I upgraded my unstable box to exim 4 because exim 3 isn't beeing
supported any longer. Debian still seems to provide security updates
for it, but it isn't beeing maintained up stream. At least the
maintainance of exim3 is what I read on debian-security-anounce.
Hope this helps.
Kenny