Although "inferior" and "subordinate" may have the same synonymous meaning, the connotative meanings are quite different.
In English, "subordinate" does in fact refer to someone who is of lower rank (within a business structure) to yourself. For example, a manager and his/her subordinates.
However, "inferior" means someone of lesser quality or character. It's a demeaning term that refers to someone personally, rather than in the hierarchal structure of business or society. For example, you would say the quality of fabric is inferior when compared to another, but you wouldn't say it's subordinate (doesn't make sense).