4.2BSD signal question (revised).

[Dave Martindale]

One possible rationale for why sending TERM and HUP to a process generate
automatic CONT signals while QUIT does not:

The INTR and QUIT signals are normally generated from the keyboard and
sent only to the "foreground" process group, which is executing.
There should be no need to send a CONT.  TERM and HUP, on the other
hand, are often sent to "background" processes because you want to
get rid of them, or the system is going down, or your phone line just hung
up - in these cases you want the process to un-suspend so it can clean
up and die.