From R side i think this is mainly because ggplot2 is really really slow.

Base R graphics would plot 100,000 points in about 100 milliseconds.

    x <- rnorm(100000)
    plot(x)

A quick benchmark with writing to a file:

    x <- rnorm(100000)
    system.time({
      png("file.png")
      plot(x)
      dev.off()
    })

     user  system elapsed
    0.179   0.002   0.180