Google bought Nest's talent not the thermostat and smoke detector...
I think Nest was under pressure from Honeywell's lawsuits and needed deep pockets to survive. Google may fade the thermostat and smoke detector in favor of other devices like Google Glass.
The entire Nest Team probably sold their souls to Google for the 3.2 Billon because it was either that or get crushed by Honeywell.
Time will tell.