A recent interview with Elop sounded like Nokia had better luck focusing on a few carriers in the US than they had with their European strategy in terms of getting carriers to actually promote the phones.
Do you really think that manufacturers design and build phones, then offer them up to the carriers?
Don't think of it being one-sided like that, the blame goes both ways. Manufacturers approach carriers w/ their roadmap of phones and the carriers decide which one they are interested in. At this point, this is when the carrier start making demands, such as exclusivity, and the negotiations begin.
If your carrier doesn't pick up a Nokia WP, then I recommend that you email the appropriate channels of your carrier and express interest in Nokia WP.