While taxiing in KSEA last night I turned on the wipers and noticed that they appear to only wipe about 1/3 of the windscreen and then go back down. Is this a bug or real world operation?

I was wondering the same thing as I noticed that last night as well.  But if you look at the wipers going while looking at the exterior view they seem to go much higher than what you see on the inside view.

The windshields are narrow and the wipers are long. They only rotate so much: http://youtu.be/Gp54Aof14CQ?t=8m18s

 

The wipers are secondary anyway. The screens are already coated with rain repellent (which is why you do not run the wipers when the screens are dry---you'll scratch the off the coating!).

I also wondered why Boeing designed the wipers like this. Very interesting.  I believe the 737 has the same kind of wipers.

 

Richard