The issue here is that Watch Dogs is a sandbox game and, as with almost any sandbox game, the majority of the 40 hour figure quoted will be spent in going from point A to point B in the city. That isn't exactly the most enthralling gameplay. MMOs also force players to slow travel on foot or mounted, from point A to point B. While it is more immersive, there's not really any more actual content than a game that loads the player into the start of each level after completing the last without the drudgery of getting to the actual "content".
Travel time in open world games and MMOs is not "content", it's "padding". Further, I strongly suspect that Watch Dogs won't have a save system, but a checkpoint system since console players apparently don't know how to save their games themselves. Taking an "average" of the time spent reloading and replaying between checkpoints and the point at which the player was made to reload is not "content" or at least new content, it's the same thing they just did already, possibly more than once.
Anyway, Watch Dogs looks interesting, but not interesting enough for a pre-order or full price purchase. Might get it in this December's Steam Winter Sale.
