[nickff]

I think I figured out a workaround..

Rather than setting a "Default Site Title", I set the homepage title in service_head.tpl since the homepage was the only page I wanted to receive this default title:

{if $main eq "catalog" && $current_category.category eq ""}
<title>HOMEPAGE TITLE GOES HERE</title>
{elseif $page_data.metatitle}
<title>{$page_data.metatitle}</title>
...

Now, the jQuery dialogs stop inheriting that default title and have their correct titles.

I still think, however, that setting the default site title should not be inherited by jQuery dialogs across the site!