What is the difference between quick bread and cake?
This question has become blown out of proportion. I was just curious- then I started getting answers that quickbreads and cake are the same thing- which they "obviously" aren't. So I started doing my own research.

Wikipedia says that the term quickbread was probably invented in the US after the discovery of chemical leavening. The Wikipedia references and some dictionaries corroborate this definition. Basically anything leavened with soda is quickbread.

This doesn't work. There are a great many things leavened with soda that can't be called quickbread. A good example is plain old white cake. Obviously this is a semantic issue but one that needed solving.

Two American cookbooks that I consider canonical recipe resources, The Joy of Cooking, and the Better Homes and Gardens cookbook, both have a separate quickbread section. In it are a variety of fruit breads as well as some biscuits and scones.

On Food and Cooking muddied the water a bit by differentiating between quick breads such as biscuits and batter breads such as banana bread. These were grouped together, however, and contrasted against cakes. This book says that cakes are higher in fat and sugar and have a more delicate texture.

Ratio, as linked in this answer, confused the terms a bit more also including a term "quick cake" but it differentiated between the different products with distinct ratios for the flour, fat, and sugar.

With several competing definitions I decided to take an unscientific poll. I called 6 friends in Washington, Utah, Georgia, and Texas. I tried to find a variety of American cultures. Obviously it is biased by the fact that I know all of them.
When asked "What is quickbread to you?" without exception all of them replied "banana bread"
When I followed up with: "What is the difference between that and cake" I received the following answers:  

"It is eaten at breakfast"
"It has less sugar"
"It is loaf shaped"
"It is more dense"
"It has a more open texture"  

My conclusion is that the historical definition of "anything with soda" is no longer useful. In cookbooks it seems to now be applied to chemically risen baked goods that:  


have as a rule of thumb a particular ratio of flour, fat, and sugar
have less sugar than cake
refers in particular to fruit breads, biscuits, and scones
generally has an irregular vs uniform texture


The popular definition (among my extremely limited, unrandom sampling) adds:


tends to be loaf shaped


And now I can sleep easily again.