I lived through that era (first K-Lite Codec Pack, then CCCP came along), but still it holds.

Proprietary or open, any visual codec is a battleground. Even in commercial settings, I vaguely remember people saying they prefer the end result of one encoder over another, for the same video/image format, not unlike how photographers judge cameras by their colors.

So maybe, this flexibility to PNG will enable or encourage people to write better or at least unorthodox encoders which can be decoded by standard compliant ones.