Why is there a 1 sec. last cell on commercial DVDs?

This question should have been asked here, but I did not find an answer, sorry for my lameity :) On the commercial DVDs, there is usually (or always?) the last cell in each title, all black, 1 second or so in length. When I do my own disks, I do not add such a cell. Both Power DVD and my stand alone player handle them just fine. Do I really need it? Why is it there? Also, on some disks, the last cell is linked to a LinkTailPGC command. Is it necessary for higher compatibility? My PGC post-commands are executed by the player even without this feature. Why is this often done? Thanks!

No, not at all. This is the last cell in the end of the only PGC in the main title. Looking at a few DVDs that I have around: A Beautiful Mind, Title 1 (the movie): Last cell #22, 00:01.00 Title 2 (deleted scenes), same thing. Mulholland Drive, Title 1 (VTS 7, PGC 1): Last cell #26, Program 2, 00:00.15. The movie has no chapter marks, so this is the only cell in Program #2! The Wall. No such thing here. The movie (VTS 4, PGC 1) ends with a normal cell, 04:21 long. This DVD is mastered in England, although is NTSC and P1, has some pecuilarities, such as the FBI warning in the end of the main movie, only 2 seconds long and coming in English and French. Is it a compatibility thing for older DVD players, now obsolete? Just guessing, but would like to know for sure :)

their are a few reasion whay it COULD be their .. but i truly have no idea ... it could be their as a marker for the guys in the editing room .. could be the 72mm -> digital conversion needs a "end of film" marker .... it could be their to prevent bleed so the first frame of the menu doesnt superimpose on top of the last frame of the scene it came from ... like i said their could be alot of reasions ... but odds are .. it's just a quark of whatever software some guy in cal. sold the major studios ( the movie editing stuff not the dvd authoring ).. keep in mind that when these films are converted , their is no 1:1 attention paid to the process of converting to dvd/mpeg format... it's not like the orgianl film when the director sits at a console and cut's pastes the frames of the film togher ( it's mostly digatal now but their is still film involved ) .. once the film has done it's round in the theators it's normly the studio that plops it down in the lap of the guys that do nothing but convert film all day .. so i would guess they have it down to an assembly line type of thing and every scent gets that black frame tacked on. like i said .. 90% of this is guess work :-)