Sigh, you know this is like beating a horse that's long decomposed and fossilized. /rant begin (stop reading now if you are a fanboy)
Sony and Panasonic have been doing tiny machines that they don't sell in the US that have amazing specs for years. They will likely almost always be better in specs, weight and size than Apple, Dell HP etc. It's the market they have. No one has room for a 17 inch laptop in japan, it would take up half your apartment and provide the heat for it too. Things have to be tiny to sell.
As for thickness vs wt, it's an important balance. But considering I put my macbook pro into a zeroshock case which doubles it's thickness, before I put into a laptop bag, I would say that there's an acceptable level of thickness. Weight is also a concern. You could make a super thin laptop out of a slab of osmium... but that would weigh like 20+lbs... be indestructable and all... but no one would carry it due to the weight.
As for random numbers on who would buy it or what not, I love how I can make up the fact that maybe 75% of you will get angry reading this post.
Apple will likely NEVER be the best in any spec on a laptop. I say this because they A. Don't make many different laptops to suit a wide variety of spec needs. B. Emphasize making a healthy profit margin on every laptop, and C. Emphasize an whole machine experience over having the best gear.
People will always talk about % reliability etc, but the numbers done by squaretrade show that apple is one of the better manufacturers but by no means the best. (hp is the worst though...)
The Vaio Z is a sexy machine. If apple came out tomorrow with one with the exact same specs and price, many fanboys would probably explode in the pants. I would buy one if I could hackintosh it as well as the mini 10v I carry as a backup. High resolution is nice, specs are nice and I can say from personal experience that the high end sonys last a long time even with abuse. The cheaper low end ones are prolly crap. I have a 5 year old TR2 which has been dropped... puked on... and more... and it still runs great... and the screen is still amazing for a 10inch laptop.
In the end no one will change their minds. Fanboys will still be fanboys. Unix lovers will still need command line interfaces. The hardest thing for people to do is to approach things with an open mind. I know this because I used to hate on macs... (but then they used to only use power PC chips). I bought a macbook thinking I would boot windows and use mac os infrequently (since they finally had the nvidia 9400, and I despise intel integrated slide show graphics) But after a bit of use I almost never boot to windows, and I even hackintoshed a dell mini to carry around. I still use windows 7 as my desktop OS, but If I had let myself be close minded and kept hating macs, I would never have found out. Now I recommend them to my family members and friends... I've even purchased 3 and set them up for family.
Why can't we just be impressed with how much sony could pack into that machine and how it was built? Why does everyone have to hate on something because you might be jealous or feel like anything is a personal attack on your computing religion. It takes mature individuals to be able to critically and objectively evaluate things they like and the competition. Apple is by no means the "truth" or source of all innovation etc. Sony was making the chicklet keyboards and ultra thin laptops long ago. Apple does a great job of refining ideas and polishing them. Let's hope that they do the same and make one based on this.
/rant end