Kinda funny, but this is one of the things I have always found appealing about Pentax DSLRs - their high ISO NR has always been tuned to get rid of chroma noise but allow luminance noise (which has a nice side effect of retaining more detail) - when you convert their jpegs to black and white, it looks like film grain, rather than the blotchy mess chroma noise comes off as looking.
the grain works best in the 3rd shot above!