At some point after that, it was marked as "closed" with no mention of why.
Note that the current MacOS behavior has all three of these awesome properties: 1) Inconvenient; 2) Has no sane workaround; 3) Different behavior than MacOS 10.1 through 10.4; and 4) Different behavior than every other Unix in the world.
The quantity of sympathetic outrage you've received may answer question #1 above.
As for the bug, my guess is that the pipe is implemented with or via the same mechanism as AF_UNIX, SOCK_DGRAM, and therefore dropping the data is allowed.