Magic keyboard and trackpad via wired connection but internal transmitter is always on and a question
The new Apple "Magic" peripherals (mouse, keyboard, track pad) are Bluetooth 4.2 or LE (low energy) devices which, unlike regular Bluetooth devices, Bluetooth Low Energy (BLE) doesn't broadcast all the time.

Basically, the device will only listen for connection requests and respond accordingly.  So, when they say it's always on, it only means it's on and listening; not broadcasting.