Here's the thing- the Fallen Angles didn't really reveal themselves until the rest of the chapter had come home, so to jump straight to that would have put the book chronologically out of sequence with the rest of the series. I can't remember though- Did the Lion return to Caliban after the defeat of Horus or on his way to Terra? He doesn't seem to turn up at the battle for the emperor's palace (due being caught up at Caliban) but the sequence is important. If he got delayed on the way to Terra is there any indication he'd chosen a faction to support? Had he opted to join Horus but arrived late enough to see the tide turn?
Oh- and no, the Emperor is very rarely quoted directly, in the same way (and I don't mean to offend anyone) that they Bible never actually quotes God- we just learn what he 'said'. If the guy is an infallible being then his dialogue could never be scripted by someone who is fallible. See?