Let us think about what it means for an object to be "Real". Real objects have real dependencies--the physics or expectations upon which they have been implemented. I'll pick an example of an object we might evaluate...how about a toaster?
You generally expect a toaster to have a power plug. But what else does a toaster depend on besides electricity? Of course, it depends on several natural phenomena--like the ability for air to transmit warmth, or for electricity to cause coils to get hot. Perhaps it seems silly to mention these things, but every dependency matters if you try to apply the design in other contexts. A toaster's dependence on gravity is important if you're an astronaut--the bread would float out unless you physically held it in the device!
Some dependencies are not acceptable. If your toaster also came with a large "adapter" that you had to plug into your oven, this would be a cause for concern! Firstly, there is the issue of awkwardness of the connection--it takes up physical space, and may prevent you from using the toaster and the oven at the same time. Also having to put some kind of heatproof tube which extends between the two devices creates another potential point of failure...which could be quite dangerous.
But conceptually speaking, it seems like you should be able to use a toaster even if you don't have an oven. Of course, you don't have to worry too much about your toaster actually being 'fake' and just being an interface to your oven's heat--because if your toaster depended on the oven's heat you would be required to attach some kind of tube carrying that heat.
Three dimensional space generally provides a good sanity check on dependencies. If your appliances were were unnecessarily depending on things they weren't supposed to, then your house would look like some kind of Rube Goldberg Device, like this one made by the Japanese to cook Ramen:
As silly as this is...we're already seeing precisely such implementations when the restrictions of time, and space, and cost of components are completely removed from a design problem. Sadly, this is precisely the situation that has arisen with computer software.
Unlike the physical world, our current operating systems don't do a very good job of letting the casual user dismantle the software they are using and understand the dependencies inside it. When you try to run TOASTER.EXE and it says you have to install OVEN.DLL...how would you know whether this is a legitimate or illegitimate dependency? To those who understand software, they understand that often programs are written with dependencies that are nearly as ludicrous...introducing bloat, limitations, and unnecessary points of failure.
When I think about the kind of illusions we might face as technology advances, the dream about Reliable Culture comes to mind. In that dream, a girl and i were dealing with a product that would taste and look like wine if you drank it straight. I scolded her for buying it from a "spell shop" because it was designed to stimulate only the "wine sense" of one's memory--thus it wasn't completely implemented with all the protocols of a liquid!
Even in today's world, it is often less expensive to get a simulacrum of an object or experience than to obtain the full object or experience itself. Yet at some point the simulacrum will break down from the reality.
Admittedly, some people might prefer the "fake"--those who purchase pornographic videos may actually prefer that to the actual reality of going through the experiences depicted. Yet by and large, simulations are a shoddy substitution for the real experience you expect. Pushing the "wine button" in your brain may be an inexpensive shortcut, but something that just pushes the "wine button" can't be used in cooking to create a new and nuanced flavor for a sauce.
So perhaps we should be thankful for our relatively stable system of physics--with only one kind of heat, and where you can't make a wine that isn't also obeying the protocols of a liquid! Living in a virtual reality will certainly open up possibilities for exploits beyond any of the deceptions that we've seen in this world.