A github account is very useful if you want to submit changes back to Kovid. Other than that, you can do everything you need to do without one. Other than submission, as far as I can see the development process is identical.
Hmmm... you would have everything except a convenient backup of your repository. Pushing your stuff to your own repo on github puts your work somewhere other than on your local disk. On the other hand, it makes that work visible to others. You pays your dues and makes your choice.
