This versus having a major failure of one of the existing satellites and having to pay big money to get a quick launch? Guess how many subs they would risk by halving their CONUS HD bandwidth for several months. It isn't like there are a bunch of Ka lease birds aloft and available to move to 103W.
I would imagine that the cost of maintaining a spare at station keeping in terms of fuel is relatively low in comparison of with what it costs to make the much more frequent corrections required for an active Ka satellite.
Since it was originally going to be an on the ground spare, it would seem that aside D10s issues, Directv agreed with me that keeping it on the ground was a better choice than having it in orbit.