The winglets on the 172 are attached to the engine cowls, I believe these are used to enhance short field take off capability. I think the original poster was talking about winglets on the wing tip. Some manufacturers believe that a well designed wingtip i.e. with sharp edges is just as effective as a wing with winglets. You probably could develop winglets for an ATR or Dash 8, however it will be a trade off between development cost vs benefits of the reduction in induced drag. Hope this helps.
CL.