The user actions that lead to mistakes in Excel are the same with any other environment: typing formulas. If I'm doing an engineering or financial calculation and misplace a decimal point, flip a sign, or forget an ABS(), I'm going to get the same wrong result in R or Excel. The upside of Excel is that the feedback is immediate so you have a chance of spotting the error if you're expecting a certain output. There is no clean solution to that regardless of environment. It's just as easy to make mistakes when you're changing code or changing a spreadsheet.
R has the advantage of being easier to do a proper diff between files if a change was made in error, but most people don't think they made a change in error. The change was intentional; they just got it wrong.