How to determine complete reverse dependencies?

[Pádraig Brady <P@draigBrady.com>]

I wrote a script on the train this morning to determine
the "complete" reverse dependencies for a
specified set of packages, for both RPM and DEB.
http://www.pixelbeat.org/scripts/whatrequires

It works as expected on my fedora core 3 laptop.
However when trying it on my ubuntu breezy desktop,
I noticed some missing dependencies.
For e.g. imagemagick isn't reported to depend on libc6 ?

$ whatrequires libc6 | grep imagemagick
$ ldd /usr/bin/convert | grep libc
        libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb7a1b000)

So I'm wondering is this a bug in the imagemagick package
dependencies, or am I doing something stupid?

I'm sorry if this is the wrong list or an obvious question.
But my excuse is that I've only been using debian for a couple of weeks.

thanks,
Pádraig.