Let's just be happy there was no 8GB version. Otherwise the 8GB would have probably started at $349 and bumped the other 2 up by $50.
The Nexus device is not really meant to compete with the S3 or G2 at this point. The Nexus device is really meant for devs to create on pure Android and Google is willing to eat profits for that. In the meantime all the non-devs and phone geeks get to enjoy a great phone at a great price.
If Google wanted to sell this phone like there was no tomorrow and compete with Samsung you would have seen some crazy marketing done by them prior to the launch. Instead, there wasn't even a peep out of Google and it silently just showed up for sale. To me that says they are not trying to take over the world with device sales.
I think their probably more interested in making profits on devices through Motorola. These are just some of my opinions and really doesn't represent anything more then that. Only Google really knows the answer to the who, what, where, when and why's. Just accept you are getting a great phone at a great price.