Sounds like a very silly question, but I tried, and it isn\'t too easy to find a simple answer to this simple question on google.
The longer story:
Before
Again, maybe not a very direct way of exporting to iCalendar, but this may help to get there anyway. I found on Sharepoint 2007 (and I am not sure whether 2010 has this feature, too, but it's quite possible), that you can create your own views of a calendar by using the "View" button and menu:
I found that MS Excel 2013 for some reason doesn't want to paste the contents of the clipboard thus obtained, but LibreOffice Calc does it just fine without any complaints. The specific calendar I exported in that way had some 1,300 events spread out over five years.