I wonder: are Apple's designs just as data-driven?
Not only that, but they are masters of creating a 'design ecosystem'. Browse apple.com, then head to the apple store, its a seamless experience. This is arguably one of the competitive advantages that has helped Apple maintain it's position in the market and with consumers everywhere.
The reason Apple's been successful is that they occupy a small but passionate niche of customers that are completely underserved by Microsoft. Most users don't care about design - but the ones that do care a lot, and will pay a premium for something that pays attention to their needs. There's probably room for a similar competitor to Google, but nobody's found it yet.
Most users don't care about design? I think the number of the different Apple products sold say otherwise. A phone that anyone can pick up and use many of the features without reading a manual, thats a byproduct of brilliant design on many levels. Whether people care or not, they connect with it and are put in a position where they now have feelings for a piece of technology. When they then decide to make that purchase they very much care about design.
Microsoft products have indeed been successful, but other than the xbox (and we're talking consumer electronics here not OS's) what has been the other runaway hit they've made? The zune is a great media player, but came about after msft assembled a team and put them in a room with an ipod and told them to make something better.
The growth in sales from Apples products combined with their increasing marketshare in the desktop and mobile spaces are very indicative of consumers demanding better designed stuff. Apple's in-house iterative process is best positioned and most efficient at making products that are in line with that.
A friend of mine, now an Apple emeritus distinguished engineer, said that during the engineering redesign of the Apple UI elements for Leopard (10.5) (which ended up looking nearly the same as 10.4), the engineers would have a weekly meeting, where they'd present just a few buttons. Jobs would walk in and say "yes" or "no" and walk out. Took quite a few iterations. ;-)
(To be clear, this was the internal re-engineering effort to make the Aqua UI resolution-independent. Inside of 10.5 is a huge set of tools that accomplish that fact, but it still had to look the same at current resolutions, and also look good at higher, which we haven't seen yet. The good results is that they can deploy a whole new system-wide, resolution-independent look & feel by replacing some XML and PNG files in the Appearance internal framework, and with no code changes. I suspect we're going to see that used in 10.6 very late in the cycle so there are no leaks.)