One of the most common problems when installing is knowing what hardware you have and what drivers are needed for them. pciutils helps resolve this by allowing users to see what their basic hardware is, however while it's on the minimal install CD, it's not included in a stage 3 install. This means that if users reboot to their install and find they've forgotten about or got the driver wrong for some essential hardware such as network devices, they can get stuck, being forced to reboot to the install CD to fix the problem. I propose that sys-apps/pciutils be included on a standard Stage 3 install to help alleviate this problem.
A stage3 install is only supposed to contain necessary system packages. I fail to see how this package is necessary for systems that have ISA, sbus, or any one of the non-PCI busses you find on older machines and non-x86 hardware. It's the same reason that there is no longer a DHCP client included in a default install.
Andrew is correct. We simply aren't taking any suggestions for expanding the stage3 tarballs with new, unnecessary packages.