I always read numbers like they are going from left to right. Like 12 is 10+2, so it makes sense to put what represents the largest number first. If 12 was written as "21", and I was reading that number in a sentence I would have look ahead a space to look at the last number first.

So I don't know what the Indians and Arabs were thinking ordering the numbers like that if they read right to left, that would be retarded.