It's not JUST that - it's also HIDs, etc.
Now you can get an Edge with the 3.7L but no bells and whistles (Sport) OR you can get the Edge with all the bells and whistles but not the 3.7L (Limited).
Or you can get the MKX which has both. This keeps the MKX somewhat exclusive while still allowing Edge buyers access to both the 3.7L and the bells and whistles, just not together.