Earlier quoted context omitted.
Google didn't argue that this patent purchase was for defensive reasons. They argued that it was for offensive reasons, that these patents could then be used to attack Google and force licensing fees onto Android. That entire argument is negated by the fact that Google had the option of bidding jointly on the patents and, therefore, having a license to them.
Google wanted the patents to fight back against Microsoft, since Microsoft is the one probably leveraging the greatest patent tax against Android devices. A joint ownership of the patents would be useless against Microsof. They could leverage them against Apple, or Oracle, or other parties that didn't own them, however, but even that could be to Microsoft's benefit. Keep your friends close, keep your enemies closer,…
Here's the problem: Even if Google won the Novell bid, they would not be able to use the patents as a defense against MS. MS is licensing the patents from Novell, and I think that if any other party bought the patent pool, they would continue to license them from whomever bought the pool. So Google couldn't use them in a defensive manner. They could make life annoying for MS by increasing the fees, but that's about it, especially because if they increased the fees too high, they'd doing the exact same thing that MS is.
Plus, I think that the DoJ's decision to put the patents under GPLv2 and the OIN patent license would have been made regardless of who actually bought the pool, considering that a lot of the patents apply to Linux. So even if Google had won, it's not clear if it would have actually helped them in the end.