The iCal file attendees are getting has a few problems.
The event is send out in the ics file as an meeting. So it is required to "send" that event to someone, or like youself. Alternativly you can save that event, this is however more complicated.
I suggest to change it to be send out as an Appointment. Just remove the "ORGANIZER" line for the ics file to get that.
Furthermore, the event description is not transfered correctly to the ics file. In the HTML body part, new lines are still marked with "\n" instead of "<BR>"
I just found one more thing, sorry 
If I organize a multiple time recuring event. As an organizer I get my mail for that with a download of the iCal file. However when opening this file it will only import the first event and not the second.
Removing the line "X-MS-OLK-FORCEINSPECTOROPEN:TRUE" will kind of fix that. But now you get it opened in a new calendar. Now I actually do not know how to fix that.