For the record GavJ has a record of starting debates, and although he's stubborn and will never admit he's wrong (if he is), he usually has a few good points. Although you can easily argue with him until the world ends... (For the record, I don't dislike GavJ, we all have our personalities, and that's just his, but when arguing with him its important to remember that particular part of his personality. Like how Quietust knows everything, and Footkerchief is the forum's search functionality gone sentient. I rant, and its best to avoid my rants.)
I would like to say that savescumming has its place. Sometimes the mistake was too small for it to be game crushing, the end too dull, or just science to be done. I definitely agree with the design philosophy of not providing a convenient way to back up your save folder.
If there was support for named and versioned saves, then most people would inevitably play DF like many other games, by creating a save whenever they're about to do something stupid and reloading until they finally succeed. That does take out much of the fun of DF, that there are actually consequences.
I also like that DF does allow a manual way to back up your saves. Its tedious, but sometimes useful, and its very much in taste with my personal philosophies (let people do whatever they want) as well as philosophy in DF (your fortress your way). People like different things, forcing something on someone so they have a "pure" experience is a lesser evil. DF doesn't force it, it just provides bias to the "pure" experience.