This makes approximately as much sense as "Apple is a one-hit revenue wonder: almost all their revenue is from direct sales".
As for their non-advert products: how big a market is the thermostat market, and what are the chances that Google will somehow screw up Nest? Google isn't exactly very good at customer service, and you need that for hardware.
As for these amazing robots, we've been hearing for 50 years about how robots are going to be making our lives easier at home, but it hasn't happened yet.
As has been expressed at various places on the web, the Nest acquisition was most likely about more than just thermostats and smoke detectors. It was probably about good consumer product design in general.