Lager yeast is very delicate yeast. It takes longer to brew and likes to be fermented at a lower temperature. Ale yeast, on the other hand, is very forgiving. It can cover up fermentation flaws because it has such a powerful flavor itself. The type of hops used is another element that differentiate ales and lagers.
American beers are lagers.
I never dreamed that German beers were lagers. I just assumed that any beer than had flavor was an ale. Most of the beers coming out of Britain and American micro breweries are ales. He attributes interest in ales by professional brewers to be economical in origin. Ales are easier to make, don't take as much time and almost double your fermentation space.