my argument would be that every computing device is/should be built with purpose and an intention. Direction and focus if you will....
Apple tends to do this. They have a pretty direct target for their devices. An ipad,air, or Mac Pro isn't for everyone, but they exist...for a good reason. They are purpose built machines if you will..
I feel PC's have generally lacked direction. Everyone just wants more power in a machine not built with a purpose. I guess what I mean by that is the design/intentions are not that well thought out on PC's it seems.
Macbook Air = great ultra-portable. If you compare it to anything else you are not making a fair comparison. Take the cost out of the equation. It is built for a purpose and it serves its purpose well.
PC's...you can get some good ones and bad ones. Lots of them lack thoughtful design (size/weight issues). Plus consumers don't get a fair shake when they go to Best Buy and are exposed to just those notebooks. Failure to see all of a companies line-up just sucks. Like sure HP has a few good gems, but Best Buy isn't going to carry an HP ProBook......