There are that many lies of CSS because there that many places the theme can be styled. There are over 400 lines to make the menus work.
Why the Twenty-ten theme, which isn't nearly as customizable, style.css file is 1324 lines long.
The more a theme is customized, the more css there is.
You can set the CSS to be in an external file, but it still has all that code, the difference is that when using external CSS, the file is only loaded to your computer once for the duration of that session. If someone only visits the front page, then it actually takes a little longer if the CSS is external because an extra request has to be sent to the server and the file delivered. You will gain that time back the more pages they visit, but unless you are serving thousands of pages an hour, i don't think anyone will ever notice.
Last edited by juggledad; Mar 28, 2011 at 06:54 PM.