So your saying:
I get home after work and decide to listen to Pandora while I make dinner. I plug in headphones, open the app and choose my station, making sure my iPhone says I'm connected to my WiFi network.
I start streamiong Pandora and drop my phone into my pocket.
By your logic, when the phone goes to sleep in my pocket, it will drop my WiFi connection and connect to LTE and continue streaming Pandora over LTE.
BUT, when I take it out of my pocket, and wake it, it reconnects to WiFi. Until it falls asleep again in my pocket and reconnects to LTE.
Yes?
I couldn't be the same problem that Verizon users were experiencing (http://support.apple.com/kb/HT5526)? Sure sounds like it to me.
PS Yes, I burning thrugh data, but I'm connected to a power source.