Unless I'm mistaken, I really don't believe it's an issue with the spec. There's nothing in iCal (RFC 5545) that says you have to take iCal objects attached to emails and automatically include them in the calendar. In fact, iCal servers are simply configured to accept the xml requests and distribute a list of VEVENT objects (among others) for display. They aren't inherently connected to a working inbox.
My guess is they have loose rules around auto-adding iCal attachments detected in IMAP/Mime messages. It's notoriously difficult to get email and calendars working. There's a reason ActiveSync is so damn expensive.
Visual Studio for Mac is a re-brand of Xamarin Studio. However, perhaps more importantly than the software itself, opening the Visual Studio brand to the mac environment signals Microsoft's commitment, yet again, to meeting developers in their chosen environment. Xamarin Studio is also based on MonoDevelop, so maybe this could accelerate a VS linux port, if they're so inclined.
My guess is they have loose rules around auto-adding iCal attachments detected in IMAP/Mime messages. It's notoriously difficult to get email and calendars working. There's a reason ActiveSync is so damn expensive.