Apple biggest UX failures always stem from putting form before function. There is a lower limit to thinness/lightness before consumers just don't care, and it was passed long ago. There was great progress made with the unibody Macbook Pros and the Macbook Airs but these latest models are so thin that it's actually annoying and leads to issues like poor battery life, lack of repair-ability, and malfunctioning keyboard…
On one hand I'm inclined to agree with you. Thin is not always better. On the other hand I'm holding my 3 pound Macbook Pro comfortably and easily. It's light enough that I don't have to think about slipping it into my day bag (something I did think about with the previous iteration) and thin enough to easily grip with one hand and walk around. When I was traveling, there wasn't even a question about whether I would…
Perhaps if it was still a netbook/macbook air product then it would make sense, but we also have iphones and ipads now which actually seem to be getting bigger so there's no reason why the most mobile powerful computing device must be so small.