While Disneylands has many of the same things, there are some MAJOR differences that are year-round. Here are just a few:
1) The Moving Room. I guess its not really that noticable to the commoner, but Disneyland's moves down, WDWs the ceiling moves up.
2)The changing picture gallery in DL. Thats way different than the area approaching the buggies in WDW.
3) The REALLY creepy pictures on the walls of the residents quarters in DL. None like that in WDW.
4)The Morgue on the way out of the ride in DL. Nothing like that in WDW.
5) The little ghost woman is projected as your walking off the ride in DL. In WDW she is seen while your still in the buggy.
6) Some of the audio track is different ("...if your left behind you may not need to apply.." or something like that is one good example.)
7) The exteriors of each are much different.
8) The library in DL is in the picture gallery, which its the first thing in the WDW while your on the ride.
...And I can think of about 6 more that I wont list because I'm probably boring you.
I'm not saying that the changes during the Haunted Holidays aren't segnificant, because I know they are. I'm just saying the difference are significant all year, making both HMs so very awesome and special!
-Matt