There are 3 types of pads, soft, super soft and hard. Those have different weights. But within a type, new ones don't weigh much different than older ones. The weight difference listed could also be due to it being the total shipping weight so the packaging comes into play.
Anyway, been sanding with Festool for 11 years now and owned 13 different types of sanders, I don't see any improvement between the pads from 11 years ago and all their "improved" pads over the years.
I don't find it worth spending another penny for a newer type and I always look for the cheapest one I can find and they all work great.