Hi EBC
I am not sure what you mean by
the VS mode is not anymore used in normal flight
but on our eurocopter, when you press ALTA it engages V/S until you are within 300ft of target. Saying that, I agree V/S is not a mode I like to use, for the reasons I stated earlier.
The point I am trying to make is that with a 3-axis autopilot neither Alt. A or IAS will stop the aircraft hitting the ground if the pilot doesn't pull the lever up enough. However, Alt. A will increase the pilot's workload making it more likely that he won't pull the it up!
A four axis machine is a completely different matter and I totally agree Alt. A is the way to go if that is what you are flying.
Cheers
TeeS