A comprehensive answer to your question is going to be a very complicated answer. Suffice it here to say that:
1) Each law passed by the parliament has a specific and defined "aims and objectives" that indicates the purpose of enacting the same legislation.
2) Broadly speaking, while Industrial Disputes Act is a disputes processing/settlement legislation, the Factories Act is a normative establishment legislation that provides for standards for safety, health, and similar related matters affecting working conditions for people employed in factories. Therefore, it is not, as though, if you are in the mangerial cadre, you have less hazards to you safety. So all those employed at the Factory (barring small exceptions as rightly pointed out by you) are given the same consideration in matters provided under the Factories Act. Here the question is NOT the status, salary or designation.
3) But in matters of processing disputes, the law makers have presumed (I wonder if rightly) that people of higher status or higher salary either have no disputes or are capable of resolving their disputes themselves. It for this reason the term "workman" is chosen and defined to indicate that class of employees who have more rights and protection than others as far as this act is considered.
4) It is a safe approach that while dealing with any matter, one checks up the provisions and the definitions before taking any positions.
5) It is possible but at least I have NOT found it necessary to list out various acts defining the terms like, "employee", "worker" and "workman". To that extent I am unable to help straight away on this issue.
November 24, 2006
24th November 2006 From India, Pune