While you are almost certainly correct you are missing the point about Google's blog post. The lawyer who wrote is demonstrably lying about the situation.

"They’re doing this by banding together to acquire Novell’s old patents (the “CPTN” group including Microsoft and Apple) and Nortel’s old patents (the “Rockstar” group including Microsoft and Apple), to make sure Google didn’t get them;"

If Google was offered a chance to bid along with Microsoft, how is Microsoft trying to make sure Google didn't get them? While it may not have been in Google's best interest to partner with Microsoft, they can hardly argue in good faith that Microsoft is trying to withhold those patents from Google in some sort of conspiracy.

Microsoft et al. don't want Google to have the patents usuable against them. Either outbidding or co-owning works.

Microsoft had enough patents that it was more important Google did not have the patents for itself than for Microsoft to add to its own arsenal.

Google might have instead accused Microsoft of denying it leverage, in the face of Microsoft et al.'s mountain of existing patents, but at the time that probably seemed a verbose way of making the same point: that Android's competitors would like to kill it with patents.

(We haven't list sight of the fact that B&N, HTC, and others have been targeted for using Android, while the same can't be said for WP7 licensees, have we?)

You assume the offer was real and made in good faith. If, however, Microsoft offered Google the chance to jointly bid without any intention of really doing so, Google's interpretation still holds.