like you say, quietly replacing 4s phones; because they know it's their responsibility, which is ok for those still under warranty, however, since the 4s came out some time ago there's a lot of people out of warranty!
similar comments from the genius as another post; conflict in the new os and cannot be fixed through software/firmware; suggests it's a hardware problem due to the conflict with the new updated OS!
therefore, as previously suggested the update to ios7.0.2 has caused a hardware conflict/compatibility issue with 4s phones, their software update has caused the hardware malfunction . . . . . and the cry is out of warranty!
by my logic they should replace phones with the issue becuase they caused it!