As I sit here tonight, working on my Zenith Universe campaign I realize that it is important for me to note there are actually 2 Zenith Universe (3 really, but let's not split hairs).
The 1st Zenith Universe is the one where the HEROIC comic (soon to be released) takes place. It is a universe of conspiracies, deep plots and long running schemes. It is not so much a roleplaying universe but more a story telling one.
Then there is the 2nd Zenith Universe (I suppose we could call it Earth 2, or Other Earth, or really whatever you like). This one is more of a universe designed for roleplaying adventures. It is a heavier populated one than the 1st and it is certainly more traditionally superheroic/comic book as universes go.
The third one is the one that I use for my homegrown campaign, but that one is somewhere between the two.
Well the first reason is that I always feel that storytelling universes have different needs and purposes than roleplaying ones. Storytelling universes need to service the story. Everything you show or do should have purpose and that purpose is to benefit or drive the story. For example, while you can roleplay in say the Star Wars universe, it is really designed to tell the story of the Skywalker family. Or how the Babylon 5 universe is designed to tell the story of its namesake.
Feel free to disagree, but this is how I see things.
A roleplaying universe is meant to be more of a sandbox. A place where players can arrive and make their mark. Maybe they will travel the world and meet heroes and villains from other places, or maybe they will stay home and just be the local super team. All options are on the table. As such the roleplaying universe should provide a jumping in point, with a nice history and a lay of the land for the players and narrator to explore as they move forward, changing the world through their actions.
Surprisingly both Zenith Universe have the same kicking off point. The death of the Guardsman.
Will character from one show up in the other? Probably as while writing I might have inspiration for a great character that I want to put in an RPG book, or perhaps there is an NPC that would perfectly suit a scene I am writing.
There are no hard rules here.
Anywho, just the musings of my mind.