Saves aren't meant as a backup, but as a way to exit the game temporarily. The pace of DoomRL is a lot faster then most Roguelikes, and games are usually measured in mere hours if not minutes, whereas a single game of something like Angband might take place over days, weeks, or even months.
Most DoomRL games, with the exception of Ao100/AAo666 challenge games, will never need to be saved at all - you simply play them through to completion in a single session.
Edit: It's worth noting that the Nightmare! difficulty mode forbids saving entirely, so even a game of AAo666 - where you have to travel through 666 full DoomRL levels without dying to win - must be completed in a single session. I've tried that before and when I need to take a break, I just keep the game open and running in the background =P saving really isn't necessary here ;)