The natural behavior, the natural interaction, with objects from the real environent and with reality itself, is very complex and has by far less constraints than the virtual reality, which is computed by computer system, which is limited itself. Even the fastest computers will not be able to cope with the (unlimited) freedom of ways to interact in reality.
It is the job of the programmer to restrict the possible interaction in a way that it is still intuitive but also in the range of the possibilities of today's computers.