I've got a number of 7480 Laptops. I've been using 2 for testing.
Same BIOS version and settings, Same OS configuration, No dock attached. both have a power brick and Network Cable attached.
One laptop will wake with the press of any button on the keyboard, the other will only wake when I press the Power button.
I'm at a loss to explain why.
Since you've tried everything, perhaps contacting Dell Tech Support for further troubleshooting would be in order. You can contact Tech Support at 1-800-624-9896 or 1-800-288-4410, or you can initiate a chat session http://dell.to/2v4snVm