Many, many schools take this blanket approach. Some goes as high as 118. In the main they use this to deter parents of children who are never going to make it into a grammar. Its not always in writing, its generally mentioned verbally at the 11 plus meeting in the summer term.
Many schools have 'shock' results and will/should still invite parents such as boysmum in for a 'chat,' regardless of their policy.
I know that many schools do put forward the advice that they will tend not to support appeals outside the standard zone (116 - 120), but what I am finding shocking is:
a) that Heads are putting it in writing in quite strong terms;
b) the bar is getting ever higher. One school has stated in writing that they will definitely not support any appeal below 119.
I am very concerned that this attitude could lead to a very serious injustice, and the only reasons I can find for it are complete laziness on the part of the Heads, or a misguided sense of "humanity" in not wanting to get parents' hopes up.
It would be nice to think that all Heads will make an exception for a really shock result, but my worry is that it may not happen. Some people, once they have gone into print, will not allow themselves to be seen to backtrack.