Some ingredients are more fermentable than others, so your recipe plays a big part of the attenuation of the yeast. Sugar, for example, is nearly 100% fermentable, while some malt extract brands might be 70%. If your recipe used more fermentable ingredients, and a highly attenuative yeast, a low FG is possible.
The lowest beer I ever had was 1.006, I believe. It was thin, but crisp and dry and very drinkable. That wouldn't work in a stout- but in a cream ale it would be perfect!