And the short answer is that they won't.
RIPS use their own dithering pattern. QTR uses our GIMP Print as its ditherer, so it supports whatever patterns the Gimp print developers care to use. Roy Harrington uses an ancient version of Gimp Print, 4.3 from 2002. The 5.0 version (now called GutenPrint) is a total rewrite, a lot more sophisticated, and considerably less grainy, but switching QTR to GP5 would require making entirely new curves. GRIP uses 5.0, but it's not ready for prime time yet. (And I think the name is going to change to WIZ RIP before the beta goes out).