Document Node is not just a pure Markdown editor, it has a beautiful HTML5 preview area, where you can see your tables in a perfect format. You can define your own styles using CSS, although we have 11 preview styles built-in.
Having said that, I think it's a good idea to give the users the option to enable padding. I will add that option in a later version.
There never be a final product for us and stop there, we will keep improving it and roll new versions frequently.