Rimfire cartridges are much more susceptible to casehead failures then centerfire cartridges, because of the hollow rim and thin case (that's where the priming compound is spun). The recessed cylinder is there to protect the shooter and bystanders in case of a rim failure where brass or combustion gasses could caused injury. S&W started the practice on revolvers in the 1930's and the recommendation is to not shoot high speed .22's in a non-recessed chamber.
Centerfire cartridges have solid heads (at least modern ones do) and aren't prone to the same type of failure. S&W first offered recessed chambers in the 1930's on the Registered Magnum to set it apart from other guns and continued the feature on all magnums until the early 1980's. Colt never bothered doing it and I think it was more of a marketing tool then anything else.
Plus, the guns look better without that big gap behind the cylinder.
