Finals 3 greens.
I teach on both slab wing PA28s and the newer wing design and I find the aerodynamic warning on a new wing PA28 quite adequate. In fact, it displays all the classic characteristics of a stall, is quite well behaved and is very docile. I recently renewed my instructor rating on a PA28-161 - the exercise I demonstrated for the test was stalling.
You may be confused about the origins of the buffet and where to notice them. You mention the PA38 which I remeber does shake at the stall. But it was designed as a trainer and this may be a deliberate design feature. The PA28 was designed as a tourer with comfort in mind. However, the buffet is there and like a lot of low wing aircraft it is first noticed through the control column as the turbulent airflow breaks off the wing and is felt through the stabilator.
When you train someone, you are not just training him/her for that one type. They will go and fly something different at some stage and need a thorough grounding in all the aspects of an exercise. It the emphasis on buffet recognition in the stalling exercise is not made because the buffet is so obvious, there is a danger it may be missed when that student flys another aircraft.