I guess I can see why a tablet would want to be thinner, you make a good point with that because of the weight, i have the iPad for two years ago, and i thought that was perfectly fine thickness wise. I used an iPad air that my parents have, and for me i think its too thin but i guess thats just me.
I think my bigger issue is with the phones, I like to be able to grip my phone when using it, i have the 4S and that is perfect IMO, I want to get the iPhone 6 soon, but worry it will be too think for me. I will get a case for it, that will add a little bulk, but I still think it can get too thin at some point.
But if the goal for tablets is a piece of paper thin, (as close as you can get) then I guess ill never be happy when it gets that close