I don't see why they shouldn't include this when they include the info when it happens for a mac. When you get a new mac or it updates, you can see that spotlight is busy reindexing which explains the slowdown. I'm surprised there is not some one sentance explanation somewhere in the phone, like "processes will continue to update in the background and phone performance may be affected until this finishes" and boom, the OP article would have never been written.