daileycon that link is for billing and shipping sections. which i can already change following the tutorial at http://docs.woothemes.com/document/tutorial-customising-checkout-fields-using-actions-and-filters/
but if you check the box in the settings to accept registrations in check out there pops up a special registration form that buyers can use to become members of the website. this form does not match your standard registration form, and also does not fall under the "billing and shipping sections" that your link alludes to or the tutorial.
in your registration page you may have fields beyond username, email, and password that you require to sign up, but all that wocommerce requires are these. it obviously doesnt look up and pull your required fields so you must reconstruct them.
i and other people would like to find a tutorial that has some code example to put in your functions to address this