Scarcity, I would think, have kept the two apart. The 300 Rowland series are seriously expensive. There are few of them about. There are even fewer H2O Signatures around. I, for one, would be very happy to pit my H2O Signatures against any Rowland.
On my Scintillas, the H2O sounds closer to real than with any other system I've heard.
BTW I don't mind the spartan appearance. I use to place record album covers over the big blue eyes of my X600.