Yes, I can still access the link for iCal Exporting as guest. I do this, starting the browser and insert the copied link url (from an authenticated session I copied the link) link url.
The result is, like described:
1. with authentication on website (it means "logged in"

, "Public Events" - all events in ics-File
2. with authentication on website (it means "logged in"

, "Public And Private Events" - all events in ics-File
3. without authentication on website, "Public Events" - not any event in ics-File
4. without authentication on website, "Public And Private Events" - not all events in ics-File
I don't understand, why I get a difference from 2. to 4.
3. is ok, because only registered user can see the events, they are not public.
Why, I do this? Because I want to have the calendar as an additional calendar on my (i-)phone. But I need all the events I can see as logged in user.
It's not caused by iphone software, I tested as well with google calendar and Thunderbird with same result.