Legally there is no difference between workers and staff. In fact you cannot see the word 'staff' in any legal document or Act. One who works for the organisation for a remuneration called 'wages' or 'salary' is a worker or employee. There are Acts which distinguish workmen 'covered' and 'not covered' and employees coming under the Act and who purely do supervisory and administrative jobs.
But in practice and conventionally, those who work for lesser amount of remuneration are treated as workers and who do mainly administrative work and are involved in supervising of job are treated as 'staff' members. A more advanced version of staff emerged with the IT boom is 'professionals'.
These are relative and will change from establishment to establishment. A Foreman, who is a staff as per above description, of a small scale organisation will be treated only as a workmen when he takes up employment in a large scale organisation. It changes from situations to situations also. It is a human nature that when the management takes disciplinary action against a manager, he inclines himself to workmen. When the economy started declining and IT sector started facing problems, much of the 'professionals' have now started thinking of any possibility of themselves been treated as 'workmen' under the Industrial Disputes Act or other Acts!
Regarding Dearness Allowance, since the DA is expected to reflect cost of living, there should not be any difference in treatment. Many companies pay DA to the workmen only because DA is a mandatory component of Minimum Wages applicable. Since supervisory and managerial staff members do not come within the purview of minimum wages, they are paid an all inclusive salary.
Regards,
Madhu.T.K