I don't know what the stats are, but netbooks (and tablets) are becoming increasingly popular. I don't think you can just default to ignoring them anymore.
I'm also glad to see the 'mobile first' idea gaining traction, with css/html5 frameworks coming out based on that. There are more and more use cases where a mobile site that gracefully expands to desktop size works out better than the inverse.
Netbook sales have stagnated and have been passed by tablets. They are expected to continue to decline.
As for tables, most users use dedicated apps so this design change won't affect them. Google usually does a custom web interface for tablets/mobile anyway to make it more touch friendly.
