This update makes no sense, other than perhaps a good will gesture to let customers know that even after almost a year, they have not forgot about the device. Also perhaps to help purge S3 inventory since not a forgotten device.
Seems a lot of unneeded fluff, not to mention the multi window app function seems superfluous and limited in function on a dual core with a small display. Seems better suited for a tablet, so fluff on the S4 as well.
Also, battery appears to drain quicker since the update. Even when not using the new fluff.
Edit: After reading about the update, I am not so sure this is as much a good will gesture as thought. Seems more to show users the new features and perhaps to tweak interest in the S4. Business and goodwill can be opposing forces to some degree.