Is there a functional reason for these frame designs dependent upon firing action? Are there exceptions to this rule? Can some one possibly direct me to a link for internal diagrams of SA and DA revolvers so maybe I can see the need for each frame style?
The 'frame style' of the single actions to which you refer has to do with the grip shape and the configuration of the part of the frame that holds the trigger mechanism.
The early Colt Walker and Dragoon revolvers (or, as Sam Colt called them, pistols) were the first; the 1851 Navy Colt was among the most numerous of the cap and ball types; and the Model P, or Colt Single Action Army, retained the style of the Navy revolver. There were similar Remington designs, both cap and ball and metallic cartridge. The Colts were and remain among the best handling handguns ever devised, at least in my opinion.
Adding the double action feature necessitated two changes: a change to the grip frame to enable the shooter to handle the much longer trigger pull; and redesigning the frame to accommodate the DA mechanism and on all but a few, the crane and swing-out cylinder. Hammer block safeties were added about the same time.
Ruger later added a transfer bar to enable their SA design to be safely carried with all six chambers loaded; their Single Six and Blackhawk design retained the SA mechanism, solid frame, and grip frame of the original Colt.
The Colt and Smith DA designs came along in the late i9th century. The early S&W DA revolvers were top-break designs, as were their first single actions.
The Colt Army, Army Special, Police Positive, and Shooting Master, and the Smith M&P and similarly configured large frame designs such as the Triple Lock, pushed the old single action out of production before WWII. It was only after the Western movie and TV craze that the old favorite came back onto the shelves.
The DA arms were far superior in terms of firepower (DA fire and rapid ejection and reloading); with the exception of the later Rugers, they were safer; and they provided the advantage of a long and heavy trigger pull that is less apt to cause a negligent discharge when the shooter is under great stress.
However, for me anyway, none of them has ever come close to the Navy and SAA in terms of grip and balance.
Links:
http://www.google.com/imgres?imgurl=http://www.peacemakerspecialists.com/art/explodedgunbig.jpg&imgrefurl=http://www.peacemakerspecialists.com/parts.html&h=861&w=1000&sz=115&tbnid=KqZBkttAHxSuYM:&tbnh=81&tbnw=94&prev=/search%3Fq%3Dcolt%2B45%2Bpeacemaker%2Bdiagram%26tbm%3Disch%26tbo%3Du&zoom=1&q=colt+45+peacemaker+diagram&usg=__0vBpGxlwN-Dmvb7JF4QaVgWtUvU=&docid=17y6lvsI1glBKM&hl=en&sa=X&ei=36zXT57DEseg2AXXu7GjDw&ved=0CF4Q9QEwAA&dur=3100
http://www.allworldwars.com/Colt's%20Double-Action%20Revolver%20Caliber%2045%201909.html