The Tikipedia theme was made following the model of Mediawiki's Monobook theme, which doesn't use any multilevel menu like PHP Layers. That's why the theme was released without such a menu.
At that time PHP Layers menus weren't so widely used by TikiWiki themes and weren't well supported in most of the themes. When we decided to upgrade the PHPL support in the themes and showcase them at this site, the code was added to the Tikipedia theme installed here. Sorry, but to tell you the truth I had forgotten that this theme doesn't include the CSS for the menu at all.
I'm working on a new version of Tikipedia for Tiki 1.10 that has support for PHP Layers menus and all of the 1.10 features like fullscreen view and Ajax, and is div-based rather than using tables for layout. This should be done about the time version 1.10 is officially released.
Sorry for the trouble.