Tim, the difference in the wood grips at the place of the mag. release button is because of the left grip has to be fixed into the frame - please check other Lugers as well for example this 1914 Erfurt:
http://www.simpsonltd.com/product_in...f39d15ef65a4f5
The wide trigger question is a good one - never got a real answer - I guess it was designed for comfortable feeling while pulling the trigger but did not allow fast handling and draw out of the holster ?