There are definitely reasons for them signing up. Among them: 1. The risk of being sued. Even if the patents are bogus, they will still lose a lot of money fro

There are definitely reasons for them signing up. Among them: 1. The risk of being sued. Even if the patents are bogus, they will still lose a lot of money from defending themselves. 2. Microsoft sweetens the deal with other business interests of theirs. For example, a discount on Windows licenses.