Leon, that phenomenom is not relegated to Greek alone, it happens in many other languages, too. Honestly, I'd say Brazilian Portuguese is the king (queen?) of that. I very rarely find a movie title which is an exact translation from the original version. That is why many people that I know (I'm originally Brazilian) actually prefer, when speaking of a movie, to use its original title, rather than go by its translation.
If you were to ask me why, I'd say that literal translations scarcely ever bear the same semantical weight than its original counterpart. For that reason, it is not only preferred, but needed, to exert a little cultural influence on the title, have it sound more native-like (towards the language in which it's being translated into, of course).
And let us not forget that English has done the same with many Chinese, Japanese movies etc. :-)
Bear in mind that I am not defending this approach, though. I'm just offering you an explanation. :)
Verberat nos et lacerat fortvna: patiamvr. Non est sævitia, certamen est, qvod qvo sæpivs adierimvs, fortiores erimvs. Seneca