Being as I'm not a New England Patriot coach or player I only know that we play variable gap-assignment fronts frequently platooning defensive lineman and linebackers with a focus on making the proper reads and playing situational football.
The same as above?
Every offseason? This season, for instance, there was the much ballyhooed switch to a more predominant 1-gap 4-3 defensive front 7 alignment as opposed to our previous 2-gap 3-4/4-3 look that we played a lot last year.
No, because they change stuff every year.
Bottom line - look at every FA we've brought in who didn't perform well here despite having had success elsewhere. Those players aren't suddenly all deciding to become bums once they get to our team. Some of them just had skillsets that were better suited towards different defensive or offensive systems.
Chad Ochocinco is about as glaring an example as you can find of a player who was elite at his position with another team but is struggling to adapt here. Look at what Maybin has accomplished with the Jets but wasn't able to do with the Bills.
Some people just aren't a good fit for a specific system. You don't rebuild your entire defense around one draftee so you try to draft the players who are the best fit for your team.
This isn't rocket surgery.