TX-Ump, while I absolutely agree with your "Don't worry ... be happy" approach, the question posed very definitely has merit.
The point raised in the OP was about consistency.
It could be argued that as is, there are two categories: HR and non-HR. Thus the two existing end-game scenarios. Plus, from a stat standpoint, there's really no difference between a double and a ground-rule double. So based on that, one could argue that there's really no inconsistency issue.
But on the other hand ... a HR and a GR double are the only two types safe hits that leave the yard and become automatic as to what the base-runners are entitled to. For that reason, it could be argued that the HR and GR double should fall into the same category for the end-game results. So in that vein, yes, there is an inconsistency.
All of which is to say ... yes, be happy, the game's over, don't worry about the RBI's. But -- is the rule consistent? Could be argued either way.
ctiger, good question. Worthy of discussion. Thanks for bringing it up.