Google is a company with severe ADHD. Consumers expect home appliances to operate for decades. That is not a good mixture. If the whole "internet of things" trend dies out and people stop buying, you bet your ass Google will happily shut Nest's servers down and leave every single one of their customers out in the cold. They've already done it.
I've got friends with home automation systems from the early 80s. They work flawlessly. You think any service or device Google sells will be functioning in twenty years? Thirty?
Call me when IBM is offering a smart hub.