Nortel patents generated less than $10 million. They sold for $4.5 billion. IDCC patents will generate $400 million next year. A 15-20X sales for a buyout is not unreasonable given that these patents don't expire until 2020-2040. It gives Google the ability to cross license with a host of other patents that they need to use.
And one more thing: IDCC has invented a new video compression technology that optimizes video delivery to mobil devices. It is going to revolutionize the market. How much do you suppose a patent like that is worth? Google owns Youtube, dude.