Actor-Inspired Element: Eddie Riggs was at first designed as a general roadie with a hint of Deadpan Snarker, and he even took after Lemmy for a while. As the character was developed, elements of Jack Black were thought of, but the designers couldn't have guessed that Jack Black himself would approach them to work on the project (he was a fan of Double Fine's previous work, Psychonauts). Eventually, Eddie became Jack.
Self Plagiarism: The Deuce looks exactly like Manny Calvera's car in Grim Fandango. Tim Schafer worked on both projects.
What Could Have Been: Many things that were planned were cut from the game because of time and budget constraints.
The story was going to be twice as long, and there was going to be a third continent that would have served as the Tainted Coil's homeland.
An AI "autopilot mode" would have been available in which Mangus handles all RTS segments.
Fleetus was going to lead a fourth faction. The Tick Chopper units were originally his, and are the only creature of his army to stay in the game. (The Tainted Coil uses them instead.) Fleetus hints several times in-game that he has a whole army hidden somewhere and they will seek revenge on Eddie. Concept art reveals he had wings like the other factions, and there is a picture of him enjoying a beer alongside Eddie, implying friendly rivalry.
Ophelia was going to stay dead. But Tim Schafer didn't want to leave Eddie alone with Lita.
A sequel was in the pre-planning stages, but was canceled after the first game's disappointing sales figures.
Emperor Doviculous was originally going to be voiced by Ronnie James Dio, but Tim Schaffer eventually decided that Tim Curry would be a better fit for the character.