A lot of printers can not be used without drivers from the printer-driver-gutenprint package. It should be added to the ISO image to support as many printers as possible right out-of-the-box. Doing so is especially relevant for the use case of generating secure off-line OpenPGP keys that one wants to backup by printing with e.g. the paperkey program (see #8957 (closed)). Connecting to the internet to install the printer drivers is not an option in this case.