It's not that there's something wrong with TTT or TROTK (theatrical v. extended), but that they're mostly similar in quality (w/o the green-tint difference of TFOTR). Therefore not worth the major effort for such a minor improvement.
Too bad for us, 'cause what we're here to do. :)

Check out Caps-A-Holic for up-close, comparative examination. Get started with TFOTR then search there for the others: http://www.caps-a-holic.com/hd_vergleiche/index.php?&vergleich=lord_of_the_rings_1_bd1

RE: TFOTR-EE green tint:
If true that Peter Jackson commanded that hideous green tinting ("source confirmed ... Peter Jackson and Andrew Lesnie not only approved the transfer but dictated the new color timing" - http://forum.blu-ray.com/showpost.php?p=4841029&postcount=2596), then he's just another George Lucas ... talent mostly lying in others who made the films.
(Nothing wrong with that, BTW. Just that he, too, must step down from the genius-filmmaker pedestal.)