If I could have put any tone into the words it would be one of curiosity and respect. Judging from the votes there are more people who read a lot that was not written.
Back to topic. Not implementing $foo-- as the inverse of $foo++ must have had serious reasons. The undeterminedness of the predecessor does not seem to qualify, because the meaning of undef is a lot closer to 'this string has no predecessor' than 'die' or '-1' (or foo). So there must have been more to it. What? Until now it's just guess and assume - and I can do no better.