It's strange to me that there aren't many options to buy phones pre-rooted. Considering how much I value my free time and how little I want to risk bricking my new device, I would easily pay an extra $50-100 for a phone that was both rooted and under warranty. I imagine even less tech-savvy people could be sold on the idea by just demonstrating the new "features" that you gain.
My understanding is that licensing restrictions prevent o e from shipping an android device that includes any of the useful proprietary bits from google, unless you are an "approved" manufacturer. I believe this is why Cyanogen mod had to make some concessions in order to ship a product that can be sold outside the grey market.