What an interesting question! Some aspects of centrosome function are indeed independent of the centrioles, but it turns out that centrioles have their own role to play in many aspects of cellular function. Experiments that have looked closely at centriole function are fairly recent and many textbooks are out dated in terms of how centrioles are described. For example, the centrioles become the basal bodies of cilia and flagella in cells that have to make these specialized motility organelles. Also, in all animal cells, the centrioles are thought to organize the "matrix" surrounding the centrosomes and ensures its duplication at each cell division. Although it is not yet exactly clear what the matrix does, cells lacking the matrix (called the "pericentriolar material") often exhibit difficulty in cell division, chromosomal movements during mitosis and in microtubule structure and function.