In the past I used to agree with your comment about duplicated tools. There are some (few) duplicated tools between PM and UBCD. But there is no coordination between the projects, so something that is now in PM might not be in the future. So if UBCD takes out some little tool and PM decides not to keep it either, then such tool would not be included any longer, at all.
In addition, the different versions might be helpful for different systems. Also, the booting methods for each "duplicated" tool are not the same (for example, PM might have a floppy image and UBCD might use instead a Syslinux module for the same tool).
You could also say the same about some Syslinux components included in both, UBCD and PM, but it would make the PM customized update even longer (more steps for customization).
The potential gain in size is very little (few MBs at best), so the additional usage flexibility and easier customizations are more valuable than re-evaluating the inclusion of each little extra tool.
Moreover, there are some DOS-based ports of some Linux-based tools that I would include in UBCD too, even if they are already part of PMagic.
For the most part, the tools are not duplicated.