My two cents would be - we need to base on something. If Matt has implemented the IOR feature and set water IOR value to 1.33 I have no reason to distrust him as a software designer.
I don't care that values are "off" or "in" as long as water looks like water and chrome looks like chrome.
A really basic way of looking at things on my part, I agree. But I have no time to delve into physics and molecular biology while working with Terragen. Enough said. Maybe I don't have enough of experience yet, but really... does anyone have a spectrometer and x-ray in their eyes to determine whether a texture is accurately represented or not?