I stand to be corrected on this but I believe the red stars are reserved for routes to which AC has either dedicated XM planes or is very confident they can supply XM aircraft for. The other routes are essentially toss-ups and while you may get an XM aircraft, you may not, and as such AC doesn't set the expectation of such.

I know that I have flown on 767 flights that while not "red-starred" online, did feature XM amenities onboard.