Ask HN: What's missing from “learn code in browser” sites?

I think increasing programming literacy is an incredibly important problem to solve. At the very least I want to help my friends in the process of career transitions consider retraining to be a programmer. So I looked online to find some examples of these "learn code in browser" sites, which should be a very convenient way to get started. Here's an example list: http://techcrunch.com/2012/08/21/5-ways-to-learn-code-from-the-comfort-of-your-own-browser/

For people with more experience using these, and teaching programming in general, what do you think is missing from these services? What would you do to improve them?

Cheers