This might sound weird, but it helps in two ways :

• [Github API only accepts CORS requests from oauth registered domains](http://developer.github.com/v3/#cross-origin-resource-sharing]. This means to setup a working app that uses basic authentication, you will still have to setup an oauth application just to whitelist your domain. I found this out when I tested my app on something other than localhost.
• Since the current github.js API does not pass the headers via callbacks, the response headers are neglected. This includes things like rate limits and pagination urls, which might be useful to developers, but are not passed. Using Jsonp would make sure that this is passed along as well.

As such, this would lead to losing nothing and making things a lot easier for the end users. For instance, anyone could just fork my repository, and it would automatically work for them at username.github.com/repo/ if I shift to gh-pages without them having to create an oauth application.