Well, it's not that it was "different" as much as it was poorer quality. Oh, unless you're referring to the newly recorded version for Paris...I'm not sure which you mean, but...
Here is something Al Lutz posted on Miceage.com that may clarify a little more what actually happened...
"it's a new sound after all
Someone was kind enough to forward the next item to me. Apparently WDI has gone back to original source recordings for the Disneyland it's a small world attraction soundtracks and music on this rehab. And unlike in the recent past, they spent a lot of time and money to get this right!
Apparently it's fairly complicated what has happened: the original 1963 tracks were recorded onto 35 mm film, from which they made mono tracks, and these same mono tracks were installed at Disneyland when the show moved. Back in the '60s the recordings had undergone several generations of dubs, so they sounded dull and lifeless ever since.
When Disneyland Paris was built, Imagineering (WDI) decided to re-record the music, but using a two-minute underliner predominantly so there was a lot of repetition. Shortly after the Paris park opened, Anaheim attraction simply took and adapted the Paris version.
As all that was going on, the old tracks were transferred to digital multitrack tapes, a project that took several years. Recently they finished, at which time they discovered that with the original masters, they could now build a new stereo mix from the originally recorded three channels.
So for the current rehab on it's a small world, they ripped out the entire old sound system and installed new equipment, new speakers (in some areas offering stereo soound), and even new wiring. The show is now as least as good as, if not better than, the 1964 World's Fair version. It's never been of this quality in the ride's Anaheim lifetime.
The kind source went on: I would never dream of telling you what to say, but I hope you share my belief that this is extremely positive and we should be supportive (otherwise WDI might not take the trouble in the future - and, more to the point, they won't be given such opportunities in the future if fans don't notice!)
First the facade gets restored, then the interior, and now the sound. I'm a happy camper. I think the customers should be too.
"