But again, why does there need to be asphalt outside the white lines on
straights 
I'm dead sure it's just manufacturers lobbying it to pass lower classes more easily...
Yes Arnage got some asphalt extension when the corner was modified in 2012 but that was relatively small in comparison to most of the new 2013/2014 pavings such as re-extension of the Mulsanne chicanes, Dunlop esses, Curves and rundown to Ford chicanes etc.
With Dunlop esses now starting to get extensions as well the only remaining large area without asphalt runoff is the large bit between Mulsanne corner and middleway of Curves (apart from said Arnage rework and left side of upon arrival to Indy). And now that will be gone too...