There's a lot of stuff inside a computer that doesn't make it to the spec sheet, and that is usually described as "better building quality". Now, we can harp on about the sexy aluminium chassis, which frankly only matters if you're treating your laptop like crap. Or you can get down to stuff that's perhaps a little less obvious, but, at least in my case, much more relevant.
When I joined the company I'm currently working for, I was given a budget for a laptop. Given that budget, I suggested they instead buy me a set of display/mouse/keyboard, and I'd use my own Macbook Pro. Some time later, after the advantages of the big display and lower-set keyboard starting becoming obvious to the rest of the company, people got upgraded to similar setups. Now, I work at a place where there are loads of power fluctuations. What we immediately saw was all the other laptops here that connect via VGA to their respective displays got serious issues with the image flickering. I don't mean a tiny flicker, I mean great big stripes visible a metre away. Disconnecting the laptops from their chargers fixes the issue, as does connecting them via DVI/HDMI where possible. The voltage regulators in those laptops' power supplies suck balls, and the noisy power is propagating all the way to the display. Me? I'm still working on the MBP, and it works just fine with VGA.
Granted, "I work in a place with bad power" isn't exactly the biggest issue in most people's minds when they're shopping for a laptop. I also agree that it's a steep price difference for "better build quality" (I still think that the buying into the OS makes it worthwhile, though I accept that others don't). But it's quite clear to me that comparing purely on the performance specs is missing some details of the whole picture.
0.1% * 1000$ * 1 transaction = 1$ tax.
0.1% * 1$ * 1000 transactions = 1$ tax.
What you really want is a fixed x cents tax, with x open to discussion. That tax puts an effective limit on the minimum margin required to make a purchase/sell pair profitable.
Top Ten Things Overheard At The ANSI C Draft Committee Meetings: (5) All right, who's the wiseguy who stuck this trigraph stuff in here?