My opening line was "for clarity, I will ignore Rebels, EOS-M, and SL-1 and concentrate on the higher end cameras"Sorry I missed that.
Weatherproofing of a touchscreen is the same as for a "normal" screen. Even articulated screens can be easily weathersealed.
It's understandable that entry level cameras do not have articulate screens for pricing reasons. However, none of Canon or Nikon's high end, weather sealed cameras has articulate screens. Only the enthusiast cameras get them: 650D/700D/60D/70D/5100/5200/5300.