In the past, many of the stainless guns had flash-chromed hammers and triggers. This was a common practice from the late '70's to the early '90's. Even then, during that era, some stainless guns were made with case-colored hammers and triggers. I don't know if the internals were ever all flash-chromed. I always thought FC was more of a cosmetic thing, though I'm sure it did add some corrosion resistance also.
S&W went away from flash-chrome and to near universal case-colored hammers and triggers from the late '90's to present. At least for standard production. Only in the last few years have I seen a small number of new guns with flash-chrome once again, so it's something that's coming back on certain stainless models.
Whether they went away from flash-chromed as a cost savings measure, I don't know for certain. But S&W hasn't stayed in business all these years, while other revolver manufacturers went bankrupt and disappeared, by making their guns MORE costly to produce.