90% usability may be a good deal, but only for the 20% of people who put the effort in to find benefit from the technology. Everyone else would have spent less, but gained less as well -- as they ignore large swaths of features, spending only enough cognitive time to use one or two core applications.

E.g. Note the incredible flexibility and power of desktop PCs and how that's been almost completely ignored by 90% of users, who barely know enough to do email and the web.

And that's a particular issue in the case of a mobile, secondary-computing device such as tablets, where having the functionality isn't anywhere near as important as actually improving the experience of using those functions.

i.e. They have passable email on their desktop and/or phone, so you need more than passable email to sell a tablet. If 'almost' having good usability was good enough, we'd have been hip-deep in windows tablets for the last decade and Palm PDAs before that.

Apple is happy owning a small market share while obtain a higher price for its items.