* Getting device metrics for Google's internal use
* DNS lookups that are only available from querying google directly - in other words, recursion is disabled for some records needed by the device
The first case should be entirely optional, the second case is deliberate subversion of internet standards.
If Google wants to sell captive toys well, that's nothing I'd ever buy, but they're free to. But it needs to be clear that it is a proprietary widget, dependent on Google's services and incapable of operating in environments where those dependencies are unacceptable.
That's in fact the approach of many printer manufacturers regarding toner/ink cartridges, and usually users complain about that.
https://github.com/iBaa/PlexConnect I’m sure some inventive person could figure out a creative use for a ChromeCast.
But overall, I agree with you.
As for microwave ovens and other appliances, if updating software is not a normal part of use of the device, then it is not a computer. In that case, I think the user need not take cognizance of whether the device contains a processor and software, or is built some other way. However, if it has an "update firmware" button, that means installing different software is a normal part of use, so it is a computer.
Many of the objections in comments to this post are expressed in terms of standards compliance or interoperability. I think it makes more sense to analyze whether it's a general-purpose PC or not.
There is both a protocol and a service associated with DNS.