In many respects, Speer was the cleverest defendant at the Nuremberg trials. He admitted to just enough guilt to gain sympathy and seem remorseful, but not to anything more.
I find it interesting that after the war the Soviets agreed to early release for some of Nuremberg criminals, but they demanded that Speer (and Hess) do their full sentences.
Yes he served his full sentence because of the Soviets.
Interesting tidbit here:
http://military.wikia.com/wiki/Albert_Speer
In 1940, Joseph Stalin proposed that Speer pay a visit to Moscow. Stalin had been particularly impressed by Speer’s work in Paris, and wished to meet the “Architect of the Reich”. Hitler, alternating between amusement and anger, did not allow Speer to go, fearing that Stalin would put Speer in a “rat hole” until a new Moscow arose.[