Why didn't they just take a few screenshots of GOG's edition and use those for comparison? Sure, the difference wouldn't have been that big, and people would've fought over whether the old style or the new one is better, but at least they would be spared another embarassing episode.
Oh, and I suspect the "missing source code" explanation to be BS. I don't see how Armageddon's Blade and Shadow of Death would have different source code, particularly since they weren't expandalones. I'm pretty certain the modders who made Wake of Gods would have been more than able to mod GOG's H3Complete version with the new content. I'm waiting for Ubi to announce that they've 'miraculously' found AB and SoD a short while after they release Restoration of Erathia HD.