Why doesn't Atahualpa use an externally named CSS file?

I have been looking at my webpage made within Atahualpa and the code behind it (in FF right click and then choose 'View Page Source'). On my website (www.elmsfarmcottages.com) it shows all the CSS code in a very long list.

Am I right in thinking that the page would load quicker if the CSS was kept in a separate external file?

Would I also be right in thinking that if it was kept in its own file only the CSS needed to load the page being viewed would be loaded, thus reducing the amount of code being read and allowing the page to load quicker?

When I have looked at other websites (again by using 'View Page Source') not built from Atahualpa often all the CSS seems to be hidden in a named external stylesheet.

I would be interested to know which is the better system.

Thanks, John