First of all, attempting to label a work as science fiction or fantasy can be fraught with peril. Some argue that any science or technology that does not currently exist in our society is fantasy, and yes that includes staples of conventional SF such as FTL drive.
Before going on, I would also like to point out that Tron is similar in some aspects to the animated movie Wreck-it Ralph and reference this question. The critical differences being that in WIR, life forms are electrical in nature (since they can travel along power cords), in the world of Tron they are entirely digital in nature as travel is via network and other digital connections.
Things that I think we have to accept up front about the world of Tron, that 1) programs are alive; 2) humans can enter the world of Tron through a digital conversion process; 3) humans how abilities in the world of Tron that programs do not; 4) Programs have characteristics of their creators.
I believe that the fact that the programs are clearly alive is an indication that the world of Tron is not a simulation. The computing technology available in 1982 would not have permitted a simulation of that scale.
It seems to me that the world of Tron must be some kind of pocket or sub-universe, contained within the "real" universe of that story. All access to the world of Tron is through that universe. If the world of Tron was a larger scale structure, it should be possible to access it from other universes.
It is a long standing meme in fantasy that magic is ultimately derived from human belief, faith or life force. It seems reasonable to presume that the world of Tron and the living programs that it contains have somehow been created by the life force of the people that worked on them. As a person works on a piece of hardware or software, they invest some of their life force in their work and that force, as well as their beliefs goes to shape the digital world of Tron.
This provides some explanation behind the digitization of humans. The process of digitization would take the entirety of a human's life force and transfer it to the Tron world. This is why humans in that world have extra abilities - unlike programs which are constructed from small quantities of human life force, the digitized humans are bundles of pure, raw human life force - the very essence from which the programs and the entire Tron world have been created.
Ultimately, many people would consider anything involving "life force" to be strictly fantasy. However, there are some works, such as Babylon 5 and Star Trek where advanced life forms can be entirely or mostly energy (Q, Organians, Vorlons) and so an argument could be made under a similar theory that Tron is science fiction. Where and how the SF/F line is drawn is a very tricky and subjective subject.