@amiloradovsky@functional.cafe technically, while addressable, the entire space might not be representable with an N bit address either. In general you would want to specify/represent it with a range, which would be two numbers, beginning and the end. In this case we can fix the beginning as 0 inclusive, and use an N bit number to represent the end, but this is still not enough, need one more bit to specify whether the endpoint is included or not
[0,N?
If, as with 0, you decide it's always inclusded - can't represent the empty range [0,0), and otherwise - the longest representable range [0,2^N-1) would be of length 2^N-1. Not willing to spare a bit, the latter is what people usually end up with, since the empty range is much more useful, than one extra memory slot. Then the same N bit number is then enough to represent the length of any representable range, without being counter-intuitive.

TL;DR - It's just a question of whether you want the empty range or the full (2^N element) range to be representable in general, address or length, ordinal or cardinal, it's the same.

Sidenote: address 0 is not arbitrary, if it was arbitrary, I would have had to specify it and use whopping 2N bits for my range representation in this trivial example. I do enough of that in real code, so thank you precious 0 for saving me the trouble.