Red Hat was the target of a lawsuit, which means trying to get the patent invalidated, as
opposed to paying the troll, is risky. The troll would be less likely to settle if Red Hat
were also trying to invalidate the patent at the same time.
Attacking a patent from multiple sides at the same time is valuable. Sun invalidating the
patent, even though there were not the target of a lawsuit, in effect helping out a
competitor, is a strong message to the trolls that they will be fighting not just one company,
but all companies affected by patent trolls. Hopefully this point does not get lost in the PR