I should rephrase my words a bit.

Web developers have a history of wanting to be able to run their html/css/javascript on as much browsers and platforms as possible without rewriting their code, they also have a history of bashing Microsoft and IE for not making enough progress with the browser. I don't see that group of people suddenly using WinJS to create html applications for Windows only. My conclusion is that WinJS will not become a popular platform to develop on.

EDIT: added a sentence