Piers:

I feel that the dictionary is a better resource for defining terms than either you or Marx. Socialism pertains to goods and resources held in common under democratic control. Communism with a capital 'C' refers to the Marxian system specifically, with all its fiddly bits of Marxist dogma, which is absent from socialism. I can give you a host of other philosophies that are distinct from Communism. There is an uncapitalized use of the word, communism, which is related to group control of resources also without dogma, and without Marx, no coincidence there.

There are even more than one versions of Communism extant, like Shiites and Sunnis, they split over leadership and descent of the leadership of the original strain. And, not unlike Shiites and Sunnis, they have been willing to kill each other over those differences, as the original Trotsky's head was split by a Stalinist assassin.

You also missed the point (not for the first time). Whether your Communist paradise workers decide to not build a Rolls or not build a Bentley, whatever device they eventually do build (Hmmm, maybe another Trabant?) will still need fuel.

Communists are so last Millenium!