Empty date archive vs empty category archive

Hi all,

I’ve noticed that if you open a link to an empty date-based archive (say, http://www.example.com/2009/ or http://www.example.com/2009/12/30/), you are redirected to your theme’s 404.php page, but if you open a link to an empty category archive (say, http://www.example.com/categories/my-category/), archive.php loads, and whatever code/markup is in the else part of your if (have_posts()) statement is executed.

Can anyone explain this difference in behaviour? Ideally I’d like archive.php to load in all cases, which would allow me to display a more useful message to the user in this else area using the relevant conditional tags for that archive type.