So far...
Hi All
That's Lineweaver's point in his analysis,that we have a very biased sample, but what we do have is enough to suggest that Jovians in long period orbits could be typical - at least 3 times the abundance of the current finds. That's ~ 20% of stars with Jovians in decent orbits.
As for "rocky core planets" well that's Io, Europa, and Ganymede... if not more. And Io & Ganymede [ at the very least ] have intrinsic magnetic-fields. Where do you get your facts from???
Mind you a nitrogen-rich atmosphere does need a deeper gravity-well to prevent loss via solar-wind pick-up. But that required mass isn't much more than Mars ~ 14% earth.
Adam