ORIGINAL: highhorse
Simple, it's for engine-out controllability. Think of it as the good engine "assisting" the rudder in compensating for the asymmetrical thrust. Did they ever use a couter-rotating (backward) starboard engine too? Less common, but it's occly done so that the "p" factor on the rt eng has less yaw moment during a slow speed high angle of attack engine out situation.
Side note: P-factor, slipstream effect and torque are commonly collectively (and quite wrongly) referred to as just torque. Torque (a rolling moment) is completely different from the other two (yaw moments), which are mostly different from each other.
Well put.
And a number of recent multi designs have much more than 2degrees. The concept for models has shown up in a number of model magazine articles, about both new designs and mods to ARFs and such. I think one model writer was suggesting 4-6degrees.