Hi – Google product manager here.
Thanks for flagging this. Our intention was to keep the plugin GPL but use of the service itself tied to our TOS. We will be pushing this update very soon.
The update will read:
“The plugin source code is GPL, however use of Google Services through
the plugin is governed by Google’s Terms of Service and Privacy
Policy. For products and services that can be used with the Google
Publisher Plugin, such as AdSense, additional Terms of Service may
also apply.”
Thanks!