For Bioconductor packages this information is available via link to the download stats page for each package. It can be found at the bottom of every package's landing page (ie. http://bioconductor.org/packages/BiocGenerics/) as part of the last table Package Downloads Report
(ie. http://bioconductor.org/packages/stats/bioc/BiocGenerics/)
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As far as I am aware, accurate download statistics are not generally available for CRAN packages because the CRAN repository has many mirrors. AFAIK download statistics are only available for the Rstudio mirror of CRAN.