Hence a tentative conclusion that system is doing this?

How did you arrive at that conclusion, given that you have two examples using system, one of them showing signs of expansion, the other doesn't? I would think that the non-expansion of perl -le"system 'type junk*'" to be a sign system doesn't do expansion.

And 'echo' doesn't expand wildcards natively:

c:\test>echo *
*
[download]

If your Windows shell is like many modern Unix shells, that will actually be handled internally by the shell, while the perl -le"system 'echo junk*'" actually calls a separate program.