ROS is a bad measure to use, as it ignore turnover (Sales / Net Assets). A much better book return measure would be Return on Investment.
Investors should also look at market measure like total return to investors. XON is about 13.6% from 1995-2005 -- good, but not as good as Hillary's investment in commodities which returned $100 on the dollar.
I totally agree with you. I used the ROS simply because the numbers are easier to find and calculate for those who don't understand the more accurate measurement approach.