Significant figures on component's values
It's pretty much self-explanatory. 

"101 ohms" could be as far off as 100.5 ohms or 101.5 ohms 1/101 ~= 1%  of nominal value

"999 ohms" could be as far off as 998.5 ohms or 999.5 ohms 1/999 ~= 0.1% of nominal value

In other words the same number of ohms represents a much smaller percentage of the nominal value if the first (most significant) digit is an 8 or a 9 compared to if it is a 1 or a 2.