You have to wonder what the nuisance factor is for a company like Samsung, Apple or Nokia when facing the potential liability of patent infringement for billions of dollars worth of product already in the marketplace.
It is likely much cheaper and more expediant to settle and license than create a long protracted court case that could create the perception of a bully in the court system and end up being much more costly, both in the form of a negative judgement and a downward pressure on the stock price.