Audio Systems: Infinity gold Speakers, wattage range, infinity gold

Question
I have a 98 Grand Cherokee Ltd with Infinity Gold speakers.  In the last year, the drivers's door speaker blew (I replaced it),   then the back driver's side passenger door speaker blew (I replaced it), then the passenger side rear door speaker blew (I replaced it 3 days ago) and then just today, the front passenger side door speaker blew!  What the heck could cause this?  They seemed to blow in a pattern around the vehicle one after another.  At about $85 a piece this is getting ridiculous.  The dealership just says that they get old and fail.  I don't believe this for a 8 year old vehicle.  Any advice or possible reason would be appreciated.

Answer
after the first one, i would have gone to another type. designers make speakers that just work in a specific wattage range, and you're just trying to get too much out of them. i suggest going to crutchfield.com and entering your car year, make and model, they will show you exactly what fits your car, select speakers with higher power handling, then go somewhere like parts-express.com where they're cheaper to buy.