Just like MobileMe, iCloud does not display calendar subscriptions (outside of the Birthdays calendar) in it's web-based calendar: http://support.apple.com/kb/HT5029. Similarly there is no interface to add subscriptions directly to the MobileMe / iCloud web calendar. This must be done in iCal or an iOS device.
These calendars still sync through MobileMe / iCloud between computers and iOS devices even though they are not visible.
Hope that helps!