Lt. Figgnuts said:
It's hard to say. I could definitely look into it, but for some reason it's Superman who is related more to Christ or a Messiah figure than any other.
Perhaps it's the very idea of Superman - THE superhero, the one every other is measured by (especially in the DCU). In some ways, a God among men, and in others more human than any earthling (which is how Jesus is popularly depicted).
A lot of it probably DOES come from the superficial - a being decidedly alien to the human race (with the Superman story, a Kryptonian; with the Jesus story, the Son of God) is sent by his father (Jor-El; God the Father) from an otherworldly place (Krypton; Heaven) to save humanity.
Perhaps its the fact that Superman's creators were both Jewish, and perhaps it is possible that the two modeled the character after their idea of a Messiah (whether intentionally or not).
Who's to say? There are any number of reasons that Superman is compared to Jesus more than any other superhero.