Not sure, but I've always mostly associated rpms with commercial oriented distros and debs with community oriented distros. At least that was the way it seemed to me when I gave up on Mandrake (now Mandriva) almost ten years ago.

The difference, at least as I see it, is commercial distros want to officially support the least amount of packages they can get away with so their users are forced to look to outside repositories a lot more often than the users
of the more centralized community distros such as Debian.

Nowadays I prefer to deal with dependencies myself and use Gentoo which streamlines the process.