Ahh, you found me... Run!
I never noticed a difference in the cardstock between first edition and the expansion, so I doubt there should be a difference between second edition and the expansion.
Nonetheless, that's the case. I used to own the first edition which had the same cardstock as the expansion, which is exactly why I'm surprised that my 2nd edition printing has different cardstock.
I am, however, perfectly capable of differentiating cardstock.