Nothing makes me want to become a rackspace customer more than posts like this. I adore integrity.
By spending more resources to not only defend themselves, but also destroy the weapon that the patent troll is using, Rackspace is advertising that not only do other trolls risk spending money in court, but they also risk the invalidation of their patents. Anyone trolling is unlikely to want to risk that.
1: http://www.poetryloverspage.com/poets/kipling/dane_geld.html
The psychology/poli-sci experts have agreed on "don't negotiate terrorists" for a reason, and I think that attitude applies perfectly in this patent troll situation.
(Noting also that there is the PR value of spending money this way as your comment proves!)
But they chose a higher road.
Obviously, I expect Rackspace to pursue its own business self-interest, but often there are multiple ways to do that, and not all of them are win-win for both the hosting company and for its customers.