"How could Dell, for example, possibly copy Apple’s operations when they currently classify “Design & Performance” and “Thin & Powerful” as separate laptop categories?"
The answer is pretty simple: the Powerful in "Thin & Powerful" is not as good as the "Performance" in "Design & Performance".
There are approximately three different categories for laptops: desktop replacements (powerful but very heavy, no battery life); netbooks (puny but very light, good battery life); and executive machines (a blend of power and weight with long battery life: Thinkpad, Portege). Before netbooks, there was another category: el-cheapo (weak and not very light, mediocre battery), but the hardware has advanced sufficiently that modern netbooks are viable web browser machines for many people who only use them for such, and it has mostly crowded out that segment. The PC laptop makers probably made most markup in the executive class segment.
Apple has similar categories, but it markets them better and even more precisely: the iPad is their netbook, the MBA their executive class, and the MBP their desktop replacement. But with the latest generations of the MBA, they've started to cut in towards the netbook market and eat into the margins PC laptop makers were getting in the executive segment.
But meanwhile, PC laptop makers were already getting burned by netbook-class machines getting more powerful. So what we're seeing is a slow disappearance of a segment of the market, and that's tripping up the marketing messages from the PC laptop manufacturers.
(FWIW, my relatively ancient Toshiba Portege is arguably a better machine than my fairly new MBA; it's considerably lighter, more fully featured, with Ethernet and DVD writer, and almost as fast. What it isn't is stylish: it compromises by being made of relatively flimsy plastic. If it were sold today, it could be made cheaply - a lot more cheaply than an MBA. But I don't think it's profitable for Toshiba to make and market it (and their later Porteges are much heavier as the market landscape shifts).