I'm gonna have to get in touch with the web team. It may be on there in preparation of the 5.0 launch, but 4.5 only supports calDav standards up to iCal.
Bummer, I know. It really should just say 5.0, and I'll let the team know.
Now, 5.0 (RC2 and Hosted Demo included) works rather well. We were just playing with it today.
5.0 is still on track for Dec.