I think we can still add a github repo 'https://github.com/appcelerator/titanium_studio' without .git extension. The reg exp also consider for .git extension in the URL.

As I am able to import 'github repository as a new project' with URL such as git://github.com/pinnamur/html.ruble

So we might not be able to validate all github repos adding through such URL (without .git extension)