You wrote:

Occasionally, I'm told "strong typing helps prevent programmer error", with no explanation of how it prevents errors. (Okay, so it stops me from adding a string and an int. If I was adding strings and ints and expecting to get something useful, I have deeper problems than weak typing.)

Please consider this C code:

char name[] = "miguel";
int st_len = 0, namel;

namel = strlen(name);
st_len += name;
[download]

See my error (actually a typo)? See how gcc warnings (which are kinda weak strong typing) save my time?