The U.S. auto industry has had one heck of a year.Sales have fallen off, credit has been pretty much nonexistant and two of the major U.S. automakers were bankrupt. Other that all that, things were fine.But Bill Diehl, chief executive of advisory firm BBK, said at theĀ first day of this year’s Reuters Autos Summit, that one of the main concerns for 2010 (if it’s not THE main concern) is the industry’s overall exposure to commercial real estate.We have been hearing about the problems with commercial real estate in many other sectors of the U.S. economy and Diehl gave the strongest statement so far about the auto side.(To hear Diehl\’s comments, please click here)The Reuters Autos Summit continues through Thursday in Detroit and Paris.