Say you have two games. One focuses on interactive storytelling, and roleplaying applies in the context of the story. Basically, choices and consequences all to different extent relate to the story. Heck, let's even take a recent example, Oblivion. Rather than making a vast explorable world, with limited emphasis on the story, you would focus on the Amulet of Kings, Boromir, etc. Only, you would turn it into a complex nonlinear story, where you could have meaningful interaction within. Got the Amulet? How about trading it to the black market? You interactions with the world would be via the story, rather than for exploration's own sake (to an extent, perhaps similar to exploring the world of Fallout specifically because you were looking for the waterchip). In terms of plausibility, this could be done quite easily within less than 20 hrs, and still provide quite a satisfying experience. Is it not a RPG if you can roleplay your character within the story?
On the other side, take Oblivion, but make it 'Bioware/Obsidian' style. Sidequests and so on, linear storyline with some sprinkles of choices spread throughout, only marginally. The main quest could take, maybe, 20 hrs in total. Only, because of lack of focus, it would be pretty linear (go to Spellhold, then go to the Underdark, then the elven city, rock on!). The difference would be that the game would be longer because you would diverge from the storyline at various points, engaging in exploration and sidequests that have no or little link with the main story.
Which would you prefer?