Why are AnsiStrings indexed from one and dynamic arrays indexed from zero in the Delphi programming language?
Is this a historical accident, to make AnsiStrings work more like ShortStrings, or is there some deeper logic at work?
One of the contributing factors that led to "Pascal" strings being 1 indexed instead of 0 indexed was that the length of the string was stored in the zeroth byte. Yes, that could have been hidden from the programmer's view by having the compiler internally add a constant offset to the string index expression (as was done in Delphi's long strings later) but in the beginning things were much simpler. Allocate a block of memory, store the length in byte zero, index the char data from byte 1. End of story.
As I recall UCSD Pascal was using this length-in-zero-byte convention long before Turbo Pascal came along.
As for why dynamic arrays are zero based, I don't recall any specific reason but I would guess it reflects the dynamic array's kinship to dynamically allocating a buffer and indexing off the buffer pointer. The array types that you would use to create array pointer types were zero based arrays. The first byte is found at buffer pointer + 0 offset. This is the C rationalization for zero based everything. There was no compelling reason to carry string's 1 based indexing pattern over to compiler managed arrays when string's 1 based indexing was already (and had always been) the exception rather than the norm.
It may well be that because the string type was the first array-like data type that everyone first encountered and possibly the most used data type across the board, there may be a perception of a bias towards 1 based indexing in the language. However, if you look closely I think you'll find arrays in Pascal (distinct from string) have never been inherently 1 based, especially when dynamically allocated.