The older 737s, the 727s, DC9s and EMB120s may account for maybe 20% of the current airliner fleet in the US, and are being parked on a daily basis...
With regard to the F18, a computer is a computer whether one calls it an FMS or an APG xx...(yeah, yeah, an integrated radar). The F/A 18 has "Flip of the switch" mission capability b/c of its FMS that integrates the air to air functions of the radar with ground map mode, and many other functions. Active flight control or dynamic instability is only a small piece of the pie.
What was stated was that just about every commercial a/c does NOT have an FMS. I disagree with that statement, and went on to clarify it by stating that it's difficult to find an new 121 a/c today w/o one, and the reasons why they are desireable.
Your statement questioned their benefit for domestic use on the airways; if your point was valid, dropping the FMS out of commercial a/c would make them cheaper - and a lot less profitable for the reasons I mentioned. Every hear of an airline ordering a new a/c w/o FMS?
Why is that?