I beg to differ with you. I feel you are confusing the Relieving Letter with the Service Certificate.
The Relieving Letter only states that your resignation dated so and so is accepted, and you are/will be relieved from the services from so and so date.
The Service Certificate generally mentions Name, Date of Joining, Last Held Designation, Date of Relieving, Last Drawn Salary, Reason for Leaving, etc.
Some organizations issue the above two documents separately, while some organizations issue one document which is a combination of both.
"Relieving letter says many things like designation, scale of pay, service period, reason for leaving, etc., whereas a termination letter does not cover all those aspects. What is the harm in issuing a relieving letter when the terminated employee fulfilled all formalities as per procedures?" - Pon