Good point, but I haven't seen this implemented well outside of Rogue-likes. The problem, in my mind, is that if you want to have a string of 20 encounters matter, but each one only hurts you a little, then:
1. You don't realize you screwed up on encounters 1 - 5 until you get to the end, in which case you have to go through the whole thing again, often repeating the similar tactics but with some slight modifications (I won't use bless this time because I'll need it for encounter 20, etc.).
2. You don't need to start the whole thing over again, in which case doesn't do much except make the last encounter harder for bad players and easier for good ones. If you're interested in throwing a curveball, some random factor would be more interesting.
Attrition works well with rogue-likes because they're random. If they weren't, they'd be painfully boring. Do the exact same thing on levels 1 - 5, then finally get to the part that poses a challenge, etc. In rogue-likes, you never know when the challenge will be, so you're always guessing and trying to judge if you're extending yourself too thin or not (hell, that's the main point).
I'm not saying that attrition can't be done well outside of rogue-likes, just that I can't think of an RPG that did it well, and definitely not the BG saga. I heard Realms of Arkania did, but haven't played it yet.