Any disadvandages if I style the wordpress align classes without img and .wp-caption prefix

You are right, you may have your own css rule not to follow 2013. I don’t think the 2013 theme is representing official ccs rule since 2013 is not from the wordpress team, it’s from Taiwan wp official. The reason 2013 is attached in the wp package is because it is a standard theme which follows the official basic rule which means just a demo theme nothing about style.

I was trying to say, it is just a demo css.

By the way the css you listed is from the official wordpress css core:http://codex.wordpress.org/CSS

And more, the other important thing of the css you post is..
It match the default post editor!(the class name will make the editor function works lol)