I assume some people here have played Far Cry 2. Of all the tedious aspects of that game was seeing your hand open a door really one of them? It takes one second to do. You reach out twist the knob, step into the next room, done. This takes no longer to open than doors do already, it just that you have a hand on the knob now.
Beyond that, this opens up the ability for a greater degree of player control for non-transitional doors. Do you want to swing the door wide open and barrel into the next room? Activate the door while running, your character swings it open and continues running. Want to peek inside? Activate while stationary and slowly press the door open, giving you a crack to peer through. Want to kick the door down? Activate the door and attack.
There's more to door interaction than just switching over to a new cell.
Yeah, I'm a fan of further interaction on door opening. I can see that some people don't want it, but room for it in future versions would be nice, assuming they take the first step in Skyrim and show some actual interaction between PC or NPCs and the doorways.
Further interaction would probably be better suited for an open-cell world, but interaction would be a good start for immersion this time around.