Running 2.6.28.10-power52 now

I do have a "side" question:
Using u-boot, I only installed the bootimage and modules. It all went okay and I could boot into power52.
But dependency problems will arise afterward (usb hostmode depending on flasher >= power51 etc.) if you don't install power-flasher and power-kernel. After installing both, the dependency problems where gone.

The question itself is: why would I need power-flasher and power-kernel (in NAND), and why do parts like usb hostmode depend on it (and not also optionally on the corresponding bootimage for example)?