Statistics and Lisp have a long, long history together. Before R took off, many academic statisticians were using Lisp-Stat, Luke Tierney's tool from UMN. Luke has now been spending time helping R, and it shows in how it is starting to adopt more of a Lisp mentality. The referenced paper also shows the Lisp background from R (and S) history. R syntax can be confusing enough; Lisp really has a learning effort such that most analysts just don't have the time to invest in it unless they were trained in it early on.