If you actually don't understand....
...then you clearly only see things from a VERY narrow and limited perspective. Why GMail doesn't cover everything should be PAINFULLY obvious. Cloud lovers fail to appreciate that everyone is NOT always connected, and everyone is NOT on a broadband connection, and some people CAN'T keep everything in the cloud, and a lot of people DON'T WANT everything in the cloud. C'mon, it's not that hard to understand.