Questions in the Census have changed over time. Some are dropped completely, other are altered. Other questions from the 1950 census that were changed include the removal of railroad car from the type of living quarters and if the home was on three or more acres. Some special census surveys have been discontinued, including the Census of Agriculture (now handled by the USDA), the Census of Religious Bodies (1906-1936), and the Census of Electrical Industries (1902-1927).
You can see questions from previous Decennial Census forms here.