I agree but if someone sued my company for patent infringement I would then attack the validity of the patent if I thought it was cheaper and I was stealing their technology. If I didn't infringe I could care less about the validity of the patent. Hey great idea but sorry we don't use it. Plus why would you initiate the fight on the premise we don't infringe but we are going to do everything possible to invalidate your patent? Simple logic says they infringe and they are going to try to use the legal system to weasel out of paying what is due.