Modern Rear Wheels ?

[cnighbor1]

I notice on a modern bicycle with rolf wheels that the rear wheel had a long spacer on non-drive side. I am use too just cone,washer and lock nut tight to frame. I looked at other modern bicycles near by and they all had some spacer length. Is it because they are keeping the flange to flange width constant over time, which somehow keeps the wheel dish angle the same or nearly the same on both drive and non drive sides
Charles