Thousands of Americans have switched car or truck brands this year as Asian makers led quality studies and offered a wider variety of trucks, according to a Bloomberg News story by Jeff Green.Asian vehicle makers are forecast to end theyear with a record 30.3 percent of the biggest market, the fifth year of gains over General Motors Corp., Ford Motor Co., and DaimlerChrysler AG.The trend hurts the U.S. makers because light trucks generate most of their profits, according to industry analysts. "This is the biggest threat to General Motors, Ford andChrysler's traditional brands, ever," said Art Spinella, an analyst with Bandon, Ore.-based CNW Marketing/Research Inc., which tracks auto trends for 1,200 clients including the Federal Reserve."If [the domestics] keep losing truck market share, they're basically doomed," Spinella remarked. "That's the only thing they makemoney on."The domestic share of General Motors, Ford and Chrysler will probably shrink to 63.2 percent for all of 2001 from 71.4 percent in 1997,DRI-WEFA forecasts. By 2010, domestic brands will fall to 57.9 percent and Asia's share will rise to 32.7 percent, according to projections.