[Vlad]

local orig = DEFAULT_CHAT_FRAME.AddMessage
function DEFAULT_CHAT_FRAME:AddMessage(msg, ...)
  if type(msg) == "string" then
    msg = msg:gsub("|T.+|t", "") -- should replace any icon tags and their content
  end
  return orig(self, ...)
end

Just an idea, you can make it into an addon using http://addon.ziuo.net/ if you like.