[triska]

Yes, such implementation differences definitely exist!

Whether one emphasizes the differences or commonalities of Prolog and Datalog may also depend on commercial interests: For vendors of Datalog systems, it may be advantageous to stress the differences. For Prolog vendors, it may conversely be advantageous to stress their commonalities.

Personally, I learned Prolog before Datalog, and it was easy for me to learn Datalog because I was already familiar with Prolog. The reason may be that I try to write as declaratively as possible when programming in Prolog, and that carried over well to Datalog too. More recently, I have also used tabling in many Prolog programs, and often obtained very general programs with good termination properties, similar to Datalog definitions.