Chuck and Nathan, the GPL V2 (under which license WordPress is distributed), kicks in when the application or library is "distributed". Hence it applies to the downloaded version of WordPress, and specifically in this case the downloadable Wix iOS app.
It does not apply to the Wix website (I don't even think there is a suggestion they are using GPL code there) nor does it apply to wordpress.com. Both wix.com and wordpress.com are "services" accessed remotely not distributed applications.
Two additional notes:
Most of what the extra stuff Automattic add to WordPress on wordpress.com is also GPL and available: either in the Jetpack plugin or for example here https://wpcom-themes.svn.automattic.com/. They have also released a number of os-level tools they have built for scaling.

Note also that the above mentioned GPLV3 (and the earlier Affero GPL) addresses this 'software as a service doesn't need to comply' issue. But WordPress does not use that license.