Joy Joy, tis tax season once again. 1120s &1065s here we come with one more around the corner.
I've always taken that it's just not necessary to boil the syrup. Not quite to the point where you wouldn't boil honey because of it's flavor loss.
Also, I think it is the IBUS, since a less sugar laden water is calculated to draw out more of the alpha acids from the hops. Since most of the hops have given it all away at the end, I usually add my fermentables then. (Though I admit to just pouring the water onto the syrup mass in the fermenter these past few batches.)