I don't think Kodak and Jobo actually say "don't pre-wet when using Xtol". What happened was that Xtol came out after rotary processing was already popular so Kodak did the testing and published times that were good without a pre-wet. So yes, that is the official manufacturer's recommendation because those are the tests they did.

Prior to that, Jobo itself tested a huge number of films and recommended a five minute pre-wet in order to bring rotary development times into line with the times recommended for inversion processing with intermittent agitation. There is nothing magic about Xtol -- the same technique works with it as well.