That's not true.Only if you insert columns or lines...
If you make the formula =SUM($B$2:$B$20) and insert a column between A and B, the formula changes to =SUM($C$2:$C$20) ...where column C was originally column B.
If you make the formula =SUM($B$2:$B$20) and insert a row between 1 and 2, the formula changes to =SUM($B$3:$B$21) ...where row 3 was originally row 2.
Relative cell references only change if you drag the formula around.
Now, all that said....I thought what you said was true. I guess it's never come up before (hard to believe with the amount of excelling I do, but **shrug**). So I checked, and tested what I just typed out.
One more caveat ...I don't know if this is an application level option that you could change to "Not update cell references on row/column insert or delete", or if "that's just the way it is...it's not an option". I didn't look through the options.