On re-reading that, maybe it's not very clear, so here goes again.
Most photo-quality printers have the following cartridges:
Cyan
L. Cyan
Magenta
L Magenta
Yellow
Black
.
Most non-photo printers have just
Cyan
Magenta
Yellow
Black
When you install the photo cartridge in it replaces the large black with a smaller black, plus L Cyan and L Magenta. This improves the colour rendition, bu the main cartridge is still supplying the Cyan, Magenta and Yellow, of which much more will be used in a typical photo.