The reason why its called a standard lens is because 50mm is closest to what the human eye sees.. (Under 50mm makes Objects in the picture look far apart from each other and lenses with more than 50mm will compress everything in the picture so that it looks like everything is close to each other..)
And the other reason could be because in the old days almost all the cameras came with a 50mm prime..
The 50mm is really simple to build because you dont have to create a special effect with the lens.. Only what is natural and what the human eye sees.. Also because of the simple construction they have a wide aperture..
The reason why the wide angle lenses are longer than the 50 is because it creates the illusion that the distanses are further apart from each other.. So a different and more complex construction is nessecary..
Longer lenses than 50mm needs to be long because they need to be an x amount away from the sensor.. An 800mm lens is so darn long because it ( not sure what part of the lens) needs to be 800mm away from the sensor..youll see the focal plane mark on your camera where the distance is measured from..
You can go to
http://web.canon.jp/imaging/l-lens/index.htmlAnd you can see the construction of all the different lenses and see for your whats up..