> Order confirmation pages are essentially a page they can return to at any point in the future without logging in.

Do they need to have the URL to do so?

Hmm, I suppose one could have a feature, without accounts, where you enter your email address and get emailed to you (at that address), your order history with links to individual orders.

I think you are right that at most ecommerce sites, registration does not provide too much value for the user (and is a barrier to sales). I know I am always annoyed when an ecommerce site asks me to or makes me register, and if given the option almost always choose not to register. (Exceptions for sites I use very regularly; maybe everyone is hoping their site will be one of these. :) )