Wow. Let me say that I am not the Anonymous Monk, but I shared this same endless pain over and over in assembling Strawberry Perl.

But it's not really the CPAN shell's fault, solely. It's module specific behaviors and Makefile.PL's. What is the fault of CPAN.pm is a totally opaque API that makes it very difficult for other things to integrate well with it.

Update:

Let me add that if the Makefile.PL or Build.PL use the prompt() routine (from either ExtUtils::MakeMaker or Module::Build), then you can have it automatically return the default value by setting the PERL_MM_USE_DEFAULT environment variable to a true value.

Update 2:

Also, Term::Readline::Perl respects the AUTOMATED_TESTING environment variable.

Of course, these only conventions, but they aren't totally uncommon.