That makes sense. When the original RoboCop movie was submitted to the MPAA back in 1987, it was initially rated X (which is now known as the NC-17 rating). It had to be edited and resubmitted 8 or 12 times before it got rated R.
If you compare the R-rated version of RoboCop to the unrated version, they have the same running time in minutes, which means only seconds of material had to be removed to get an R rating.