Why doesn't Shimano use shadow technology on road derailleurs? Shimano has been using their 'Shadow' technology on their high-end mountain bike rear derailleurs (> Deore) for many years.  In addition to the benefit described in the images below (from here), Shadow derailleurs have a more direct housing routing near the derailleur, which results in a lot less cable friction, and therefore, better and smoother shifting.




Why doesn't Shimano use this technology on their road rear derailleurs?  Interestingly enough, SRAM also went out of their way to avoid direct housing routing near the rear derailleur when they came out with their road derailleur, even though they'd been using direct routing for many years on their mountain bike derailleurs.
Simple answer would be that it's heavier, which is very important in road-bikes.

Regarding the cable friction and smoother shifting, road shifters are going towards electronics