It's the very, very old contradiction between convenience/features on one hand, and security on the other.

The more convenient something is, and the more features it has, the easier it is to hijack it.

They aren't fully identical, though. On my motherboard with some Realtek 8xx chip, plugging headphones into front panel jack, green jack, black jack and everything else produces progressively worse quality. Mainly bass suffers and only when driving headphones (no problem driving amps) so either these outputs have lower power capacity on the chip or DC blocking capacitors on the motherboard are smaller.