Amazing that Rome made it onto Netflix. I always assumed HBO had most of the rights to the series. But I guess the BBC owns a good chunk of the show too because there is no way HBO likes this.
I doubt HBO has a distribution channel in the UK, so they most likely sold the rights to highest bidder.
Sky Atlantic hold all the rights to HBO shows in the UK: The Sopranos, Six Feet Under, Game of Thrones etc and seasons are made available On Demand through Sky. (except from True Blood which is contracted to FX/FOX until the end of its run). Sky have also never shown Rome on Atlantic
Seems like BBC have the online/TV distribution rights to Rome even though the DVD/Blu-ray is released by WB/HBO.