The reason for this banning revolves around the game settings. In CoD 4, you fight a group of "Al Mujahedeen" somewhere in the Middle East (which, in the censor's eyes, is so wrong). Assassin's Creed is set in Jerusalem during the Third Crusade... Enough said.
The reasons are, of course, strongly correlated with religious factors. God of War 2 (PS2) was banned as well. I suspect it got banned based on the name alone. On the other hand, violent games such as Grand Theft Auto 3 are sold in the open to everyone (children and adult).
Sometimes, things get out of hand. Back in 2001, everything related to Pokemon was banned. The reason, you ask? Some wacko came up with some insane stupidity claiming that the names of Pokemons are derived from Hebrew. Here are some examples from the claim:
Pokemon means "I'm a Jew"
Pikachu means "Become a Jew"
Charmander means "God is a miser"/"God is weak"
People here, in case you were wondering, have an aversion to Jews. Clear racism if you ask me. What many fail to realize is that Judaism is not merely a religion but more like an ethnicity/race/culture. You can have a Jew who is an atheist and so on. Ignorance is blind, I guess.
But I diverge, anyhoo.. back in the day, the Internet was relatively new and everyone just down believed it everything on it. The topic caught fire and it was only a matter of time before the religious authorities issued a statement of banning.
What's next in line? Metal Gear Solid 4 (PS3) is a 'solid' candidate since there is a Middle Eastern-themed stage in the game. So, who knows?
No foreign sky protected me,
No stranger's wing shielded my face.
I stand as witness to the common lot,
survivor of that time, that place.
- From 'Requiem' by Anna Akhmatova