In a particularly poignant analogy at the D8 conference in 2010, Steve Jobs compared tablets to cars and PCs to trucks. As the market for tablets has matured, we’re seeing more differentiation between different sizes of tablets. Clearly, Apple started with the 9.7″ iPad, which still retains the main iPad branding proper with the smaller iPad being dubbed the mini. That latter device competes with a host of inexpensvie 7″ Android tablets that grow in number while shrinking in price.

Starting with a 10″ device allowed Apple to significantly differentiate from the iPhone in terms of size and the MacBook in terms of user experience. Had Apple started with the mini, it would have been harder to encourage developers to create more robust apps, something that Android tablets continue to struggle with. But, among users, the temptation is strong to turn the iPad into a faux PC, the new netbook. And indeed, this is the main thrust of the approach — encouraged by Microsoft’s positioning — that PC vendors pursue.

The adoption of smaller tablets has been driven in large part by lower prices, but also by greater portability and practicality. They have replaced e-readers for books in many cases, and are large enough to handle the recreational tablet staples of video, games, maps and books. They haven’t been as great with the Web, but higher resolution is helping with that as well. They are becoming the sedans of the Web while larger tablets are the minivans; they can be pressed into service to haul a bunch of cargo and get things done, but they’re not built for industrial duty.