ACMS
I think the whole point that 120.4 is trying to make is that if you can't do the speed, TELL ATC!!
If your company A/C have to fly a specific profile then let ATC know; they can then incorporate that. What is galling is when you tell a pilot to do something, something which you are basing legally required separation on, the pilot reads it back (which is in essence an agreement to comply), then does something different.
Radios are there for a reason!! It's not that busy in the cockpit on finals that you cannot state if you can't comply with instructions (if it is then that is a flight safety issue and should be addressed)
Omnidirectional737
The Mode S shows actual IAS, not the figure set (therefore we can see the speed bleed off as you slow down to the given IAS). It is only the Selected Flight Level that pops up straight away (we still use mode C for separation)