It is the same concept of OEM and ODM
All DTH operator in our country, are not original owner of the BOX, they all put their own firmwares to these boxes.
2. They have contract with the manufacturer {factory}
3. Maximum HD set top box have same features. Even u have FTA/Paid.
~if u have chip knowledge then u can easily understand,
For example fast charging in phone
In same processer u have seen , some devices has fast charger , some don't, due to its client, if client want they will, if not they will block this feature.
Same term in set top box
In short all dth are ODM and
Manufacturer are OEM.