The intro to this awesome post sets the stage perfectly:
The web has changed immensely in the past 20 years. In 1996 there were roughly a million websites; now there are more than a billion. Back then there were roughly 50 million internet users; today there are more than 3 billion. We have more content than we ever dreamed was possible. People are enjoying it on 8.1 billion connected devices, including more than 24,000 distinct mobile device types.
We need progressive enhancement and we need to look beyond our technological bubble. It’s good for us and it’s good for the Web.