Excellent question. The main reason is that GitHub is great for free public repos, which I generally like having as the default, and using GitHub also enables a

Excellent question. The main reason is that GitHub is great for free public repos, which I generally like having as the default, and using GitHub also enables a Secret Bonus™ at the end of the Git tutorial. When it comes to web apps, though, it's better to err on the side of security, so in that case I recommend using free private repos at Bitbucket. (These choices were made mainly because public repos are free at GitHub and private repos are free at Bitbucket. Both services are great and are definitely worth paying for, but in a free online tutorial I prefer to recommend things that are also free.)