A different, and more detailed albeit slightly dated, feature comparison can be found at CMS-Matrix.
In general, WebGUI tends to bundle the most-used features, whereas WordPress leaves most of them to plugins. WordPress does have a vibrant plugin and theme community, but they are often outmoded and of varying quality.
WordPress, hosted on typical Shared or VPS
WebGUI typical V8
Theme files, written in PHP
None by default. Built-in jQuery conflicts with Bootstrap.
Partly, built-in PHP
MySQL, possible PostgreSQL support
Web Server Linkage
One WP install can serve multiple sub-sites, but many global variables mean unrelated virtual hosts require entirely separate installs
Object-oriented, so theorietically possible to have a single installation serve unlimited unrelated virtual hosts
Particularly Moose attributes, method modifiers and roles.
Plack::Response and Plack::Request objects