1) GM Law is 18 years old.
2) I cannot speak personally about why the table was done in the manner it was done. Nor where they got their data or formula from, but suspect that it was from even older data (from printed books most likely, since the internet was still relatively young back then and very few ICE personel of the time were computer/internet literate) which could have been updated or changed any number of time since then.
3) Rolemaster is first and foremost a game. It was never intended to even closely model reality. Any "realism" to be found in Rolemaster is purely coincidental (and pure serendipity for those who like realism).
4) So the table isn't accurate according to CURRENT data/formulas? Not really a problem. My suggestion?
Chill out! Relax! Enjoy the game....
5) You want to use the table arakish posted? Great! Have fun with it!
However, ICE is unlikely to change it, since it has worked well enough for 18 years. IF/WHEN we rewrite the book, or do a variant for HARP or RMC, then we will likely use more up to date data.