One of the characteristics of a "disruptive innovation" is competing against non-consumption, rather than other products. Some people who might like to have a regular full featured laptop might not have enough money, so their choice isn't "netbook or laptop," but "netbook or nothing."
Here's a nice string of anecdotes about tech non-consumers who are lusting for iPads, but the thing here is that they aren't people who couldn't buy other computers because they were poor, they didn't want other computers because they knew they were pieces of shit. They are more demanding consumers, and they required a sustaining innovation (in usability, etc.) to consider buying a computer.