Question, what does R do that other lingos cannot?
Nothing. I'm sure other languages can do everything R can do.
Does it just have statistical functions built in and ready to go?
It does have that, along with an active community and growing popularity in scientific circles, so there is lots cutting edge interesting work being done with R -- and a lot of its free and open source. Plus it has multi-core support in several libraries places, and even gpu support in some.
since it has cutting-edge stat functions that's plenty of functionality that R has that other languages DON'T have.