The Chromecast does not operate over a local connection. It is actually operated 'through the cloud' - if you are controlling your Chromecast, you're sending operations to your Google account over the internet, which are then relayed to your Chromecast which is also tied to your Google account. Note that Google supports a non-cloud dependent sort-of-alternative for Chromecasting called Miracast in AOSP.
Android Wear is heavily dependent on Google Now, Google Search's voice recognition techniques. An Android Wear device cannot do anything without access to Google's services - it is far more than 'somewhat dependent'.
So yeah, both are in Google Services because they actually fully depend on Google's services.