Your position within our universe is giving you a bias toward one side of a mostly symmetrical situation.

Let's throw out the terms "real" and "simulated" universe and call them the "parent" and "child" universe.

Gravity in the child universe doesn't affect the parent universe, true; creating a simulation of a black hole doesn't suck the simulating computer into the event horizon. But gravity in the parent universe doesn't affect the child universe either - if I turn my computer upside-down while playing SimCity, it doesn't make my Sims scream and start falling into the sky as their city collapses around them. So instead of saying "simulated gravity isn't real because it can't affect the real universe", we say "both the parent and child universes have gravity that only acts within their own universe, rather than affecting the other."

Likewise, when you say that you can't point to the location of a gravitional force within the simulation so it must be "nowhere" - balderdash. The gravitational force that's holding Sim #13335 to the ground in my SimCity game is happening on Oak Street, right between the park and the corporate tower. When discussing a child-universe gravitational force, it is only necessary to show it has a location within the child-universe. For you to say it "doesn't exist" because you can't localize it in your universe is as parochial as for one of my Sims to say you don't exist because he's combed the entire city from north to south and he hasn't found any specific location with a person named "dfranke".