Well, there is a value proposition in the $550 iPad 3 for many people, enough people for Apple to profitably sell it at that price point. Some folks find it easier to use, with more apps they care about, and so forth. Enough that they're willing to pay the $150 premium over the Nexus 10. I personally don't consider the premium worth it, but enough other people do, and that makes all the difference. Apple is making something that people want, at a price they feel is fair.
Let's see, one of the first hits on Amazon for a core i5 ultrabook is this, at $584.98, as opposed to $1088.99 for the Surface Pro. It has a Core i5 processor, same as the Surface Pro, also runs Windows 8, same as the Surface Pro. It has 500 GB of storage as opposed to only 128 GB on the Surface Pro. It weighs 3.96 lbs as opposed to only 2 lbs for the Surface Pro, its touchscreen probably isn't as good as the Surface Pro's, and the Surface Pro's screen resolution is higher at 1920x1080 vs. 1366x768 for the VivoBook, and perhaps the battery lasts longer, but that's about it. Frankly, I don't care about these advantages enough to pay $504.01 for them, and I frankly haven't heard any convincing arguments anywhere to justify that huge, huge price difference. I could buy two VivoBooks for just a little over the price of one Surface Pro! The fact that they don't seem to be selling very much either makes me believe that more people have my opinion than disagree. Microsoft is perhaps making something some people might want, but at a price they cannot really justify.