Bonnie, I appreciate your comments and the link.  Always nice to have this kind of input and follow up.

I really don't dispute that the LSRR methodology is more comprehensive and is bound to produce more accurate and meaningful results.  But human nature being what it is when it comes to personal finance my suspicion is that for many people (if not most) the quality of the data will be the weak link.  Between the willingness to commit the time and the ability to reasonably estimate their current and future scenarios the margin of error can be significant.  Which is why the replacement ratio exists or persists - it is relatively quick and easy to compute and provides individuals with a general guideline of where they should expect to be.  

For my own purposes I have always employed an approach that would be closer to the LSRR - but I am fairly confident that I devote a lot more time to personal finance than the average person.