Some #R #rstats about the packages on the repositories: #CRAN has 722 packages that use Bioconductor (3%), #Bioconductor has 2802 packages that use CRAN's packages (77%).
1.3% CRAN and 0.6% Bioconductor respectively use package outside these two repositories. But 91% and 93% use packages on their respective repos. 8% and 3% do not have any dependency on external packages (but could depend on system dependencies).