If you have a nice fat profit margin but nobody wants to buy your product, that's no good. If you're selling lots of products but making no profit on it, that's no good either.
But if you're like GM, and you're selling millions of units a year, each for tens of thousands of dollars, and you're still not making a profit, I think we can diagnose the problem as being in the margins, not in the sales.
Seriously though, if you want to go on a whine about how bad American cars are, I suggest the comments at autoblog.com which are suitable for that kind of inanity. But for this site, I have to say that the sales figures don't support the idea that demand for GM cars is small.