I'd argue that particular storyline, while passable in a vacuum, showcased, in the treatment of Galactus, how Aaron would later behave with Thor and Odin. Galan is, simply put, out of character; his stated motives for coming to eat Earth run directly counter to the friendship he shares with more than a few Earth based heroes (including Franklin Richards who we know will survive to the end times) and the promise he willingly made to spare the planet. Likewise Odin's characterization was revamped because otherwise he cannot be the foolish, senile tyrant to oppose Jane's progressive paragon.
I'd hazard the guess that, since in King Thor #4 Thor is poised to be the cause of the destruction and subsequent rebirth of the universe, Galactus, whose entire purpose in the cosmic order was exactly that, had to be removed by poisoning via Necrosword. To be honest I'm glad Cates' upcoming run, Immortal Hulk, and History of the Marvel Universe (where Galan lives and is in the process of achieving his role) have relegated that future to alternate timeline and thus separated it from 616 Galactus altogether.