If you look at Sixto's Most Excellent Historical Records of Directv Channel Changes Q4 does look fairly quiet for HD additions.
SonyHD was added in Q4 2010, so it's not out of the question. And with all the rebalancing of transponders and such, there's hope that the wizards behind the curtain are making more room for things that will amaze and astound us. So keep your fingers crossed that October will be as boundiful as July and August were.
Well... many contracts end on the first of the year (and I believe this year it is Discovery Communications and CBS, so we may see a bunch of mudslinging right after Christmas) and that might have something to do with it. They will have already started preliminary negotiations and new HD that might be part of upcoming contracts might just be put on hold until the contracts are secured again.
Since Discovery Communications is coming up..... OWN, Investigation Discovery, and The Hub are three stations (and perhaps more, I didn't do a lot of investigating) that are owned or operated by Discovery Communications, and currently only in SD on DirecTV. It isn't unrealistic to think that Discovery might attempt to secure HD coverage of these networks during negotiations.