It's a hail mary manuever trying to, basicaly, flip the poker table over.
Since MS isn't doing anything that any other patent holder isn't doing, a B&N win on those terms would efectively end patent protection altogether. There are plenty of people that want exactly that but precious few courts willing to go along with it.
And invoking antitrust against MS to defend a Googgle product...?
Good luck with that, B&N.