Tire troubles with 2005 ST FOCUS

2005 Ford Focus ST. Bought used with 22,000 miles. Notice vibrations from the rear a month later after the purchase. Asked the dealer to check the tires and all bearings. They said the bearings were fine but the tires were seperating causing the vibrations. New tires, balance, and alignment. Next day back into the dealer for the same vibrations. Now they notice a small flat spot on the lip of the aluminum rim. "Sorry we missed that". They said thats another $300. They tried to show me the flat spot but I just couldnt see it.
Held off on rim hoping the vibration would get worse so we could pinpoint it easier. 20,000 miles later vibration stays the same. I have Firestone install a new rim. Same vibrations. They checked the rotors and bearings and everything is fine but they said the tires are badly cupped and asked where I purchased them. They also said the Focus is bad on tires. They suggested rotation every oil change.
So what ideas do you people have out there before I take a chance on another set of tires. I drive 100 miles a day all highway for work. Since I work for Ford they want me to tell everyone how wonderful thier products and service are. Just cant do it.
Any ideas would be very helpful.
Scott

Here are my favorite Focus all season tires 5 years and going : http://www.tirerack.com/tires/tires.jsp?tireMake=Pirelli&tireModel=Winter+210+SnowSport I rotate them once every two years and they are just fine!!! Solid tire