I'm surprised to hear a recommendation to rehydrate at 100F. While I do boil my rehydration water to help sanitize it, I do let it cool to room-temperature before adding the dry yeast.
I've done unscientific trials on hydrating and not hydrating and have come to the conclusion that I get significantly better performance when I hydrate the yeast. I can understand that you could easily screw up the rehydration process by not properly working with the water, but I still think that we are better off with rehydration. The reduced osmotic stress placed on the yeast due to rehydrating with plain water just makes sense to me. Sugar-filled wort places more osmotic stress on the yeast, and I can imagine, does reduce the overall viability and numbers for the yeast pitch.