Quote Originally Posted by Aralith
roomaji (the Arabic letter representations of Japansese hiragana and katakana)
You mean Roman letters. The word "romaji" itself is an abridgment of "Roman ji," where ji means characters.
Unfortunately, the Japanese katakana has not yet come up with a symbol to represent the "th" sound (and probably never will because the Japanese people can't pronounce it anyways)
They're perfectly capable of doing so. It's just not intuitive. Same deal with English-speaking people trying to roll their Rs.