It seems like GOG has a very old version of this game, because in Episode 1 LeChuck isn't voiced by Earl Boen.

As an indicator of how old that makes this version, by the time they made Episode 5 they had managed to recast the role with Earl Boen (the original VA from Curse, Escape and the remakes of 1 and 2). While he was recording his lines for Ep 5, they got him to record lines for Ep 1 and subsequently added them in an update.

I know all of this because I was active on Telltale's forums way back then. The fact that GOG's Ep 1 is missing Earl Boen is a sign that it's an incredibly old version.

Interesting, might be worth contacting GOG support about. While they read Forums, it is faster to directly get in touch with support.

Sadly there is no other online version, not even the version which was downloadable from the Telltale site contains the new voice (Telltale never bothered to release any patches for their games). Only the DVD version contains the new voice. It's just a 45 MB file however, easy to replace.

The game build was just updated. It has Earl Boen in Ep 1 now.

That's great news indeed. Now I can scrap my DVD version :D

I said that because the new version really was sold nowhere. Telltale didn't offer it for download (trust me, I tried), Steam didn't have it, GOG neither.

The only place it was available was the english DVD version which you would only get by preordering the game.
So there really was no legal way to get that version anywhere.

What GOG got now is the DVD version, also the savegame directories were changed. Whoever is publisher now, must really like us.

ps: If the english DVD was sold separatly at some point or DVDs in other languages would also contain the english voiceover, then of course there were ways to get it. But as far as I was aware, the english DVD was only available for preorder and never hit the stores.

Btw, the version with the original voice can still be downloaded from the Telltale site, if you bought the game there. Not sure about Steam. But on the latter site you can download any version in the game's history anyway. I wonder of that would also work for GOG or if they delete the old content permanently.