Italy is closer to the equator and everyone knows that gravity is stronger there...hence shorter people. Even the leaning tower of Pisa is being gravitationally challenged and it happens to be in Italy. Midgets and pygmies live right on the equator so my reasoning is sound.
It might also have to do with the density of the bones in your head. If you have a bonehead then you will be shorter.
On the other hand nations that have the propensity to have a vacuum in their heads tend to be taller because of the "lift" that they experience from childhood, due to lack of weight in that region of the body.
So closer to equator + bonehead = short farther from equator + empty head = tall
I have another theory. In the Northern Countries like Finland and Poland, the tall guys with the long legs could run faster through deep snow. Hence, they were able to chase down the girls and have sex with them, thus passing on their genes. But then some of the smarter, shorter guys invented snowshoes that allowed them to float over the snow and compete with the tall, albeit dumb guys, for the ladies' affections. The short, stupid guys just died out. So, what you now see in these countries are two distinct groups: tall, stupid guys and short, smart guys.