For tablets the picture is similar to the above, but numerous Chinese makers also use Rockchip and Allwinner devices by the shed load.
The distributors for both of these chips offer reference designs and provide design support and the end purchaser gets tied to that distributor. So most are making tablets that are essentially exactly the same. However, you cannot get the chips outside of China. The distributors just don't exist.
Well, why would you want to get those chips outside of China? If you're making cheap tablets / phones, you want to get as much of your "raw material" from the same place, and you'd be likely to be producing in China (maybe Malaysia). If you're producing a high-margin product where you can afford to manufacture in the west, you're probably using a more expensive chip, right?
We are building a very low cost, but robust device. In trips to China, we have found that unless we have representatives there, we CANNOT hold assemblers to the standards and legitimate parts and assembly quality we want. During tours of assemblers, we often ran into situations where ESD grounding didn't test on the foot straps used and they went "oh, well" lets get on with the tour.
Assembly staff was minimal and equipment poor, compensated by very large rework and testing departments. Doing it right would have cost less, if labor wasn't so cheap. As long as it works when leaving their factory, they couldn't care less if it fails due to ESD stress in a year after release.