Stratfor.com presented this useful map in a subscription ad. It more or less speaks for itself. The intra-European topological connectivity for the North German Plain shows navigable rivers (and connecting canals) permeating the landscape. Italy has only the po' Po. Navigable rivers reduce transportation costs by oodles (a technical term meaning "lots"). Even more so did they do so before motorized land transport and paved roads, let alone air-freight. But nothing moves bulk in bulk the way river barges do.
France and the Low Countries (the "Nieder Lände") do not do badly on this score, either. Note that Germany has no rivers that are entirely in Germany, while France's major rivers are entirely within France. This is one reason for the historical difference in emphasis of the two state's economic policies. Note, too, that any attempt to enumerate Europe's river valleys will encounter an Aristotelian infinite regress. No other region on earth is so geographically separated and knit together at the same time; which may be why Europe churns with commerce, but not political unity.
But there are a few questions:
1. What about Little England? Stratfor's question was only why Germany specifically is richer than Italy specifically. When we take a broader look, there is a second factor: specific coastline. This is the ratio of the length of coastline to the area enclosed. Western Europe in general has the highest specific coastline of any place on earth, excepting the island archipelagos of SE Asia. Thus, Western Europe has the highest specific coastline of any substantive continental landmass (6 x 10-3 km-1 vs. 1.7 x 10-3 km-1 for Asia).
Specific coastline plus the lengths of navigable rivers for Europe is 9 x 10-3 km-1, compared to 1 x 10-3 km-1 for China, and 5 x 10-4 km-1 for India. That is, Western Europe is nine times more topologically connected than India or China. (cf. Nicholas Rashevsky, Looking at History Through Mathematics.)
2. Specific coastline? This is more difficult to measure than you may think. coastlines are fractal, and with an infinitesimal measuring rod, all shorelines are infinitely long. In fact, that undulatoriness (a term I have just coined because English doesn't have enough words already) also comes into play: a straight shoreline is "shorter" than one with many bays, inlets, points, and peninsulas. Africa has a long shoreline but very few harbors, and so its coast is "smoother" than Western Europe's. Also the escarpment comes nearly to the shore, so that most African rivers coming down from the hinterland encounter daunting waterfalls, cataracts, and rapids that impede navigation. Ever wonder why the Nile and the Niger were homes to Africa's main civilizations?
3. Hey, Didn't Rome Used to Rule the World? Sure, and wasn't Italy richer than Germany during "the grandeur that was Rome"? How come, Mr. Geography Guy? Simple to say, I answer. It's that specific coastline thingie. Lay a grid over the whole Med basin. Color in red every grid square that contains a segment of shoreline. OK? Now color in green all those grid squares which, as the center of a tic-tac-toe pattern, have a majority of red squares among their neighbors. (Note that not all red squares will become green!) Call this the "littoral econiche." (Why not?) You will find that it pretty much matches the distribution of Greek city states and colonies, including even Marseilles and the Crimea. This is why the Eastern Empire was the economic powerhouse of Rome, why the Empire split in two the way it did, why Belisarius' reconquista went so far and no farther, and why places like Sicily and Venice remained nominal Byzantine exarchates in a Germano-Western Sea.
4. So Why Isn't That Still the Case? Two words. Allahu akbar. During the "glory that was Greece and the grandeur that was Rome, the Mediterranean was a highway. After the first two jihads, it became a wall. All the Mediterranean islands, from the Balerics, through Sardinia, Corsica, Sicily, Crete, to Rhodes were conquered by jihadis. The historian ibn Khaldûn bragged that "the Christians cannot float a plank on the Mediterranean!" This was Not Good insofar as Western trade was concerned. So the Roman gold solidus, which even Charlemagne (aka, Big Chuck) had still used, disappeared from the West, towns rotted, and the Dark Ages actually became very very dim, because as fast as the Franks and Saxons could write things down, the Saracens, Vikings, and Magyars would come and burn things up. Even Iceland and Ireland were raided by Saracen slavers. Meanwhile, the Vikings took advantage of those navigable rivers and long coastlines to keep the North in turmoil. However, once the barbarians were converted (or, in the Saracen case, repulsed), Europe developed new trade roots (that's a deliberate misspelling, folks). In place of the now-forbidden Mediterranean routes, the Europeans developed new ones in the North. Poorer to begin with, they bootstrapped. Look at those rivers above again and think "Hanseatic League."
Northern Italy is wealthier than southern Italy. What do the poorest parts of Europe -- Spain, southern Italy, Greece and the Balkans -- have in common. All were once ruled by muslim imperialist-colonialists; and dhimmis seldom prosper. But even so, it was the conversion of the Med from a highway of happy commerce to a war zone that destroyed the Southern prosperity of antiquity.
5. Bonus maps from Stratfor.
When the agricultural regions and river systems of North America are overlaid, we find that the largest contiguous agricultural region on earth is permeated by the longest interconnected navigable river system on earth. There is no similar congruence anywhere in the world.
Russia has numerous rivers, and the Volga-Don system is highly connected and embraces the Ukrainian breadbasket. (A littoral analysis of the river system picks out the distribution of the medieval Russias -- and the Moscow-Vladimir region has the highest topological connectivity.) But it drains into the landlocked Caspian and the Ukraine breadbasket (and the Don) is now independent of the other Russias. All the other Russian river systems drain north into the Arctic. So Russia has no ice-free international ports. And Siberia is not famed for its agricultural fecundity. Any questions why Russia has always been inward-looking and isolated?
Commentary on these matters are here: The Geography of Recession