This is due to primarily to advances in technology (more reliable ovens, manufacture/availability of food molds) and ingredient availability (refined sugar). When removed the icing cooled quickly to form a hard, glossy [ice-like] covering.
Although both terms can be used for savoury preparations (meat cakes or vegetable gateaux) their main use is for sweet baked goods.
Cakes can be large or small, plain of fancy, light or rich.
The first gateau were simply flat round cakes made with flour and water, but over the centuries these were enriched with honey, eggs, spices, butter, cream and milk.
From the very earliest items, a large number of French provinces have produced cakes for which they are noted.
Casse-museau is a hard dry pastry still made today'...petits choux and gateaux feuilletes are mentioned in a charter by Robert, Bishop of Amiens in 1311." ---Larousse Gastronomique, completely revised and updated [Clarkson Potter: New York] 2001 (p. The original dividing line between cake and bread was fairly thin: Roman times eggs and butter were often added to basic bread dough to give a consistency we would recognize as cakelike, and this was frequently sweetened with honey.
Terminologically, too, the earliest English cakes were virtually bread, their main distinguishing characteristics being their shape--round and flat--and the fact that they were hard on both sides from being turned over during baking..England the shape and contents of cakes were graudally converging toward our present understanding of the term.
Thus Artois had gateau razis, and Bournonnais the ancient tartes de fromage broye, de creme et de moyeau d'oeulz.
Hearth cakes are still made in Normandy, Picardy, Poitou and in some provinces in the south of France.
In medieval and Elizabethan times they were usually quite small...
Cake is a Viking contribution to the English language; it was borrowed from Old Norse kaka, which is related to a range of Germanic words, including modern English cook." ---An A to Z of Food and Drink, John Ayto [Oxford University Press: Oxford] 2002 (p. English borrowed gateau from French in the mid-nineteenth century, and at first used it fairly indiscriminately for any sort of cake, pudding, or cake-like pie...
Most were probably rather sickly, made from cheap sponge filled with 'buttercream'..coated with fondant icing. French gateau are richer than the products of British bakers. These products naturally relaxed into rounded shapes.