^^Yeah but there's no denying that steel holds up better in the long run. Aluminum simply has a shorter fatigue life(look at handguns with aluminum slides or frames, bicycles with aluminum frames etc).
Ice Cream is a pretty poor analogy if you ask me. The main ingredients of ice cream are milk and eggs...then you add the flavoring...well steel and aluminum are each made of different properties.
Also it should be noted that the 590A1 is only different from the 590, in that it has a thicker walled barrel, metal safety, and a metal trigger and guard. The internals aren't any different or made to a higher tolerance.
The 870P, however, is made to a much higher tolerance and actually has different internal parts than other 870s(ie stronger springs and a few other stronger parts).
I do like the pakerizing on the 590A1 better. I'll give them that.