What's the obsession with thin and light stuff?

I see it everywhere, people are complaining that this or that device is too thick or too heavy. For example the Lumia 920 is "too heavy" and "too Thick", but come on you can't carry something that is .42 Inches thick and comes in at .41 lbs?

I'm not going to directly say that these people are mostly out of shape but it seems that the U.S. is the fattest country in the world by a long shot and thats where the people wanting stuff to be light reside for the most part. I put 2 and 2 together.

Now, I know there's a difference between being comfortable and not being comfy, but come one, my keys are heavier than the Lumia 920.

The Surface RT is thinner and lighter than the iPad, now who cares about that? or That the MB Air is .5 pounds lighter than another Ultrabook, unless you physically cant bear it, it shouldn't matter for the most part.

I remember when I was a kid, my back pack was full and heavy, now kids have some feathers in their back packs, Im afraid of this "being lazy" trend.

Basically, What I'm getting at is, what is a good reason to want something so thin and light?

NOTE: This post is not about the Lumia 920 it's about all the gadgets that "have to be Thin and Light" in order to be useful. i.e. The first iPod Touch, so thin it was uncomfortable to hold in the hand.