Github will automatically recognize your educational email account if you have an educational email account. The problem for people taking a Coursera class is that they might not be enrolled in any school. I don't think that many of those students need to upgrade to the Bitbucket student account where they get more than 5 users.

It is pretty interesting how people are using version control in these classes. Here's one that distributes the assignments as a repository on Github[1]

[1] https://github.com/uwescience/datasci_course_materials