"Let's face facts: the Web will never be the dominant platform." Hewitt's post hinges on that statement, presented without supporting evidence. But actually the Web is already dominant among the platforms Hewitt mentions (Web, Windows, iOS, and Android). Relevant stats: Web - 1.7 billion users as of July, given that 880 million people go to the single busiest website publicly measured by Google, and this site has a "…
Lets assume iOS/android users also have a full computer. Right now i think this is reasonably accurate. So that means all the web users are also computer users. What OS do you think these people are using??
Do you honestly think that the number of people with exclusively OSX/linux outnumber the number of people with unconnected windows PCs? There are a lot of rural areas in the world with poor connectivity, and a lot of people with incomes that make the cost of connection prohibitive (while old computers are litterally dumped).
Having said all that, it matters little to the developer, because those unconnected windows users will be almost impossible to reach and won't have the money required to make development viable anyway.
TL;DR: More people on windows, but doesn't matter.