Google doesn't need to make money off of the Nexus line. But they are fighting the good fight, pushing against big carriers who continue to overcharge customers and increase profit margins without improving reception and customer service. This does come at a cost--I think that support for phones bought from third-party carriers tends to be dismal--but I can only hope Samsung, Apple, Microsoft, and others are listening. HTC and Motorola are certainly starting to listen. When an amazing flagship phone like the N6 is sold direct to the customer--undercutting its competitors' prices by hundreds of dollars--I believe carriers will start to listen. Either they'll change their ways or more and more customers will start to abandon them.
This is a long battle but I'm glad to see that Google is at the forefront of it. Here you have a company with billions of dollars of revenue and capital using their money to innovate and change the industry. I'm not wearing rose-colored glasses here--I realize how much of an uphill climb this is and I do see the drawbacks of alienating so many customers who do not know of a world beyond the traditional carrier framework--but I appreciate the innovation.