[Esel Mann]

You'd be surprised even with the battery strap, aka clip, how many attempt to connect a 9v backwards. Because the 9v battery could be put in backwards and the unit powered on, one would hope that they put a simple diode inline on the circuit board to protect from a reversed battery.

Looking at the battery compartment at the lower end there is provision for the shunt connection for a 2 AA arrangement. So it is entirely possible the battery compartment supports a couple of different applications. Some use 2 AA's, others 9v batt types. Using the leaf contacts means less different parts to manage and reduces costs by using such across multiple product lines.