I think up to some price point people ceased to care about fuel economy and diesel makes less sense....I think that point is about where the E class/5 series diesel sits....
We(North American) are generally lacking in diesel options IMO in smaller cars. The mid-range car we can get them in diesels now if you buy European. Big diesels(Q7 V12, Tourag V10...etc) are probably niche even in EU that it makes even less sense here.
University of Toronto Formula SAE Alumni 2003-2007
Formula Student Championship 2003, 2005, 2006
www.fsae.utoronto.ca