Google kicked off the Nexus program back in early 2010 with the Nexus One. It was a fine phone for the time, but it's vastly different than the most recent iterations of the Nexus flagship. That's illustrated quite well by this quick GIF.
You're really reminded of how small a 3.7-inch screen is as you watch the N1 morph into the much larger phones. It's also interesting to note that the overall aesthetic of the phone silhouette hasn't really changed much since the Nexus S.
Just relax and watch it for a while. We've come a long way, baby.