The Nexus One costs about the same as the iPhone to produce, yet the unlocked version is sold by the the same price that what an unlocked iPhone would be.
You can't buy an unlocked iPhone from Apple in the US. You can buy a contract-free iPhone for $600, which is more than the Nexus One and still locked to AT&T. Yes you may be able to unlock the iPhone yourself, but that gets you in a constant cat-and-mouse game with Apple who considers you a criminal at that point.
No non-technical user in his sane mind would pay $330 more for an unlocked phone.
T-Mobile's plans are $20/month cheaper if you're not paying off a subsidized phone, so you'll more than recoup the cost difference of the unsubsidized N1 over two years.