Here's another way to think of it:  

The call s[i] raising an IndexError isn't a numerical error, it is a conceptual error.  Knowing that i==15 and len(s)==10 doesn't usually help resolve the problem.  The fix typically isn't replacing s[i] with s[i - 5].  Usually the issue is usually deeper than that.

Note, this is different than KeyError where misspellings are common and where the fix can be indicated by knowing the key:   d['missteak'] -> d['mistake'].