If you want M::B to do exactly the same as EU:MM why bother?

I don't bother. Other module authors do, though. As for why it matters: I'm a stickler for backward compatibility and tradition. That and I'm afraid of the Perl module build process being mutated into something like the GNU autotools suite. If you've ever tried to run an autogen.sh on a BSD system, you know what I mean. If you don't, search the FreeBSD mailing list archives.

Think about it this way: I'm so pleased with the user interface of the current system that any sort of change bothers me. :)