As much as I liked Ultimate Peter, I really did feel like his series had gotten pretty stale and it would be really cheesy to bring him back. It's not that I'm entirely against characters being brought back ever, but it'd just seem really stupid and weak in this case. If it was a clone with his memories, maybe, but even so....they made such a huge thing over his death and it was so....final....it'll just seem like bad storytelling just to satisfy people's need to see their favorite character again. A lot of my favorite Ultimate characters have died (Cyclops, Beast, Nightcrawler, Peter) and I just don't want them coming back unless it makes sense storywise and doesn't seem like a cheap cop-out. And as much as I miss those characters, Spider-Man and X-Men have both been pretty damn good and re-energized by the switch.
Part of what I like about the Ultimate Universe is that they can take chances and kill characters and push the limit. It makes it very unique from the 616. And while Peter may be gone in Superior, anyone who thinks he's gone for good is nuts. 616 Peter will never actually be gone permanently (nor should he be). But it seems dumb to undermine so much of the Ultimate line's uniqueness and daring to pander to nostalgia. "But we like Peter" isn't really enough of a reason to write some contrived BS to undo the past two years of stories. Like I said, it'd just be cheesy.