Hi Eddy,
Delta DTP - Just picks the latest requests which was not updated to further. if your delta was initialized with some selections,here also same just picks the latest requests which were not loaded to further.
Selective deletion - its just deletes the data from info provider as per selections.
Delta dtp works based latest request which was lied at PSA. two of them are different activities there is no dependance.
Even DSo or Cube - Delta dtp functionality is same. works on request basis.
Thanks