Now some time later person 'c' also invents X and gets sued by person 'b's company. (or the holding company that bought out person 'b's company's IP portfolio).
Engineers have been told to literally "file a patent on everything you do, regardless of how novel or patentable you think it is, let the lawyers figure that out." further, to protect themselves they pay 'bonuses' for filing. Its a strategy and it pays dividends in the current climate.
So I understand Marco's and others frustration here, I would be interested in clearly bogus patents that have been filed post 2005 (my thesis is that starting in 1995 the PTO was hit by a zillion new patents and it wasn't until 2005 that the examiners had become trained enough to recognize the obvious ones and discard them) I've done some expert witness work and found that the prosecution histories of patents show a significant improvement in the examiner's responses as you move from 1995 to 2005.
Mandatory arbitration (prior to trial) might also be an interesting alternative, especially with the burden of proof on the plaintiff.
Precedent counts for a LOT when it comes to resolving any legal issues, even if the precedent is settling, and the trolls know that and use it.