It isn't added traction that causes the torque steer, but the diff design putting more power to the slower turning wheel (the inside wheel). This characteristic gives Torsen equipped vehicles a firm centerning feel when driven in 4A. Something that is not felt in open diffs in typical AWD designs.
this is also why i have an open on my other 4wd vehicle.
with the iwe setup on the f150, the torsen diff wont effect anything in 2wd. but if you were spinning everything all the time, will create some minor tugging .