Sadly w3schools has some serious SEO-mojo enough to win out for a lot of search queries for basic reference in html/css/javascript. At least we can be thankful experts-exchange has seemingly gone away.
The purpose of this curriculum is not the be-all and end-all of all HTML & CSS learning resources, it is focused on created a pathway that students can use to measure their learning. We are definitely focused on improving the curriculum and providing alternative resources for students to the learn from all the other resources.
I wouldn't be where I am in my front-end development without all the free and paid resources online devoted to HTML & CSS, but it would have been really helpful to have something as organized as this to guide my development.
edit: site is nice though.