Why use R?
For Kevin Goulding, the reasons also include that the freeness ensures he can always use R (no licence expiry worries), the information is great, it works well with LaTeX, there is always more than one way to accomplish something …
For monkeysuncle, the reasons also include that training researchers on free R rather than expensive licensed software ensures their continuing ability to use the skills they learn (even if there is no money for licences), plus: R is used by most academic statisticians – benefitting from their innovation and attention; it is platform independent; the help resources are unrivalled; it is easier to teach writing code than menu button clicking …
For Alasdair Sanderson, the reasons also include that it is a mature, widely used, frequently updated, free and open-source application.
For Joshua Ulrich, the reasons also include that R allows you to integrate with other languages (C/C++, Java, Python) and enables you to interact with many data sources: ODBC-compliant databases (Excel, Access) and other statistical packages (SAS, Stata, SPSS, Minitab).
A quick overview in the NYT quotes one of the co-creators of R on the ethos of R:
“R is a real demonstration of the power of collaboration, and I don’t think you could construct something like this any other way,” Mr. Ihaka said.
And here is a long list of praise for R.