Sounds like some people were hit by a bug, but this:
'the law firm says the defect occurred when a user streamed "high volumes of data" for 10 to 20 minutes. In this case, the GPU would take over all video decompression, decoding and presentation to the display. Because of this, the CPU was not needed and would go to "sleep" to conserve battery life.'
is a completely bogus explanation. A high volume of data would mean the CPU would be busy running networking code and thus would be very much needed. Among other things it'd need to do with the screen on and the phone in active use. No way is the CPU going to sleep the cause of switching from WiFi to cellular.