This part I AM NOT CONFUSED about -

I also weighed the current 1pc unit (from an Extreme Weather 300WSM) and the aluminum PT&G unit - only 1.3oz difference.

There is a difference in the "steel floor plate" between the old 2pc and he new 1pc I guess, as the difference between the current 1pc and the PT&G aluminum 1pc is only 1.3oz - weighed 'em both last night again to verify!