I agree with you but I would say that we are selecting developer instead of combat system. 
For example there is no good reason to regroup Icewind Dale 2 that is based on the 3rd edition of D&D with Icewind Dale 1 and Planescape: Torment that is base one the 2nd edition like the Baldur’s Gates series (they differ a lot in matter of characters progression). 
Also the combat system of DA2 is an excessively simplified version of the one of DAO and I would definitively not classify them together.   
It would make much more sense to have the following categories: 
- Baldur’s Gate 1, Baldur’s Gate, Icewind Dale 1 and Planescape: Torment (based on D&D 2nd edition) 
- Icewind Dale 2, Neverinter Night 1 and Neverwinter Night 2 (based on D&D 3rd edition) 
- Dragon Age Origins 
- Dragon Age 2