It doesn't surprise me to see that the 2007 model is the most popular. I think that awareness of the model got greater in the 2006/2007 timeframe after a series of consistently good magazine reviews on the 1050cc bike, so sales momentum picked up.
An additional factor was the fact that a lot of dealers, mine included, were significantly overstocked with '07s when the news of the '08 model came out. There were some pretty good deals out there as they tried to unload the older models, I got my '07 in May of '08, with a low interest rate, some free gear, and - due to the fact that they were overrun with white and green versions - a free set of bodywork because I insisted on a black model.