[luatex] Why is --progname needed?

[Karl Berry]

    necessary to write "restricted \write18 enabled." or "\write18 enabled" 
    when shell_escape is set to p or t in texmf.cnf?

"Necessary" doesn't enter into it, of course it is a deliberate choice.

Personally, I think \write18 is worth the extra line.

However, I think the other similar lines (about %&, etc.), can be
omitted from the terminal output and just written to the log.  I already
made that change for some programs and communicated with Thanh and Taco
about it.