Clive Thompson explains:
[Google Calendar offers] a strange waste of space, forcing you to look at three weeks of the past. Those weeks are largely irrelevant now. A digital calendar could be much more clever; it could reformat on the fly, putting the current week at the top of the screen, so that you always see the next three weeks at a glance. Why don't computer calendars work like that? Because they're governed by skeuomorphs – bits of design that are based on old-fashioned, physical objects. As Google Calendar shows, skeuomorphs are hobbling innovation by lashing designers to metaphors of the past.
The Dish 