well, if Ben and Chris liked the way it ended (due to the misfortunate accident with the tape), i think it's clever on their part. it left them with an option that they probably didn't think of (when they initially constructed the arrangement of the track).
@kornypony: why on earth are you comparing Portishead with DCFC? Neither group invented the abrupt ending, so just because both happen to have songs that feature them, it doesn't mean there was any competitive intent.
i found it interesting comparing the abrupt ending of this song to the one in "Silence", the first song on Portishead's new album, "Third", which was released 2 weeks ahead of Narrow Stairs. No offence to DCFC fans (for I am one myself) but I would say that Portishead used the sudden ending with much more artistic connotation. IMHO Pity and Fear would sound better fading out.