All these comments indicating "everything matters" are correct but they are missing the essence of the OP's question I believe. He wants to know why many of the higher end preamp designs only use a pair of gain stage 6922's for instance while a manufacturer like Cary or Manley will use an all-tube design with pairs of input, driver, and output tubes combined into the design. I think it's an interesting question and suspect their are schools of design in play here as well as cost of components.
