Like tmptmpgo I consider datalog something different entirely and worthy of study in its own right; a small kernel (or toy) language that by itself is not sufficient for many day-to-day tasks.
It is enough to cover relational algebra with recursion fixpoints. This gives us a handle on SQL queries. What we want is a well-behaved, predicable mix of programming and those relational operations. We have to end this SQL madness.
IMHO, it is undeniably true that Prolog is one particular way of achieving such a mix (and standardized etc), but it is not the predictable, easy-to-use and well-behaved mix we want. We should be able to isolate syntactic fragments where it is easy to ensure safety properties, at the minimum the datalog fragment. That is why having a fragment correspond as close as possible to textbook Datalog was a design constraint for me.
That said, when we talk implementation, there are of course a lot of optimizations that apply equally to Datalog and Prolog, say the magic set transformation.