I have a 4" Ruger Police Service Six, and I compared it to a picture of a 4" S&W Model 10 with Bull Barrel. It looks like the only big differences are the longer cylinder for the .357 chamber, and the ejector shroud. The two guns are very similar. They look like brothers or something. I'm surprised that S&W didn't accuse Ruger of outright copying their design. A very successful design too.
Externally, they may appear similar, but internally, their parts are VERY different. For instance, the Ruger uses stainless-steel coil springs throughout the mechanism, where the S&W uses a mixture of coil and carbon-steel flat springs. The Ruger can also be field-stripped without tools, just like most autoloading pistols; try doing THAT with a S&W revolver! Probably the most obvious external difference is the cylinder release button, which slides forward/rearward on the S&W, and presses into the frame to release the cylinder on the Ruger, but you can only see that from the left side view of each handgun.
The intended use for this type of handgun drove the basic features (during the revolver's golden age, most police/security forces wanted a 4" heavy barrel, .38/.357 caliber, and a reasonable grip size), but how each manufacturer got to the final product was up to them.
Dang it, too slow. I have to practice typing faster, and not getting distracted by other things while typing a response!