OK maybe St Andrews #17 may not be the ideal example to debate this, as it's an uphill shot which is just about at the 24inch elevation (maybe 2ins more)
Using another example, Bethpage #15, if you go long from the fairway with the pin at the front is an example of a "3ft" downhill putt. That 3ft could be anything from 31-41 inches which even on fast greens makes for challenging guesswork. You're pretty much resigned to having to chip from the rough to save par.
As WGT has introduced the Tour Legend tier with players having to putt on glass like greens, it would be helpful to have all elevation changes in inches on the greens.