I used to run a game using the old DC Heroes system, but set in a world of my own creation. For the most part, it was a ‘typical’ superhero style world, however:
1 ) The only characters who wore anything resembling a spandex costume were either funded by an outside source(like the team that was part of the Superhero Reality show), had powers that they used to manifest said costume (matter manipulation, magic, etcetera), or were considered loons. Most wore leather or denim jackets and pants with boots and gloves, plus some kind of mask, and usually colored said jackets with either leather dye or fabric paint if they were cheap. Many, however, had absolutely no secret identity, and had no more need of a costume to identify themselves than Tom Cruise or Angelina Jolie need one.
2 ) All of the non-magical super powers were automatically considered to be psionic in nature, which itself was eventually revealed to be just the flip side of magic. The limits of what a Metahuman could do were based on the amount of energy they could tap (which could grow with time), and how they percieved their powers. It was extremely hard for someone who developed, say, the ability to fire plasma bolts from his open palms, to ever do anything at all (even related to the plasma bolts) without completely and utterly changing his or her worldview and self-image.
3 ) Every single superhero team in this world was funded either by a government, a treaty group, or the UN, with the exception of a group of heroes who had pretty much no facilities beyond the SUV owned by one of them - which was a normal SUV. Individual heroes would occasionally be funded by a corporation, but usually in that case would be required to not only keep their reputations spotless, but also act as an advertising spokesman for that corporation.
4 ) Most major world powers required any metahuman running for any political office, even Dogcatcher, to publically reveal his or her powers and full identity before beginning any campaigning. Captain America couldn’t run for office, but Steve Rogers, recipient of the Super Soldier Serum who had formerly been operating as Captain America, could.
5 ) While ‘combat level’ super powers, basically enough to make the recipient combat capable in a superhero world, were rare, about 1 in 100 people had “spot on the wall” type powers - very limited things, like the ability to feed off the radiation from a television or CRT screen, or the ability to rotate their waist 270 degrees in each direction. There was absolutely no genetic cause for superpowers, as nobody knew HOW they had began (except your friendly neighborhood Game Master), so prejudice against metahumans was considered somewhat ridiculous. On the other hand, such minor powers did destroy the careers of most stage magicians, as people began thinking, “That’s probably his power” rather than “Wow, he’s good, I wonder how he did that!”
6 ) On the magic side of things, it was actually the Celtic pantheon that first sent a member back to Earth to see if the magic had returned enough, yet. Manifesting a physical avatar, Goibhnu the Smith helped found the UN’s primary superhero group, U.N.I.O.N. And very shortly thereafter, a new brownstone appeared in Soho, and the man living in it called himself the Thaumaturge - supposedly the first mage to return in full power since the return of magic in the 50’s. However, purely magical superheroes are still rare - beings both malign and benign are still too leary of Earth’s magical fields fading away again to really start getting too invested here.
7 ) Most aliens have either roughtly the same number of powered individuals as humans, or none at all, depending on how much their culture believes in or even has legends about magic, heroes, and so forth. For the most part, Earth is considered a nice place to visit by the more civilized species, and there’s even embassies for the most prominent of them scattered around the globe. However, there are still aliens who do attack Earth - not for anything Earth has, but as a way to attempt to ‘‘bloody the nose’ of a stellar nation they don’t like that has ties to Earth. Such attacks might be considered declarations of war by Earth, but little more than rogue terrorist actions by races off-Earth.
8 ) There’s probably more, but it’s been 10-15 years, and I’ve slept since then… 
Can’t think of any more others, though…
