::foresees the inevitable debate that always stems from this particular topic::
Actually, it is good to add indian almond leaf to any betta's tank, not just those used for fighting. However, the reason isn't toughening the scales so much as it releases tannins and other chemicals found naturally in the betta's habitat that promote good health. There are trace minerals and antiseptic properties found in IAL-rich water, which aids in healing. Obviously in fishkeeping, the closer we can get to the natural habitat of a species (or their ancestoral species), the betta.
As for fighting... obviously biting and body blows make up most of the activity. What is important to remember is that fighting fish selectively bred for heightened aggression and strength is much different than the natural behavior; Betta splendens do fight in the wild, but have the opprotunity to hide or escape, and do not tend to be as powerful or as exceedingly aggressive. So, when fighting fish in captivity, you get a mixed bag; some will definately have the standard situation of damage done between fish, with one eventually yeilding. Or you will sometimes get a situation where one of the fish dies, either from the injuries, the exhaustion, or the infections afterwords.
I am under the impression that most do live when fought in the traditional style in Thailand, but fighting for betting purposes has been outlawed to the best of my knowledge in that country anyways. Which leaves us with plenty of idiots in other countries who think fighting is "cool" buying fish from overseas and doing it the "wrong" way (obviously, one could say any fighting is the wrong way), resulting in the losing fish being killed.
And there are always the dimwits who throw pet store bettas together, which is ridiculous since they really have no shot of coming out of it ok; they're always in unclean, cold, unsuitable conditions in stores, and haven't been conditioned to recover from those kinds of wounds, so they typically die. I have taken on a few bettas I found in the same cup in pet stores, and it took plenty of effort to recover them from the damage they sustained; they are simply of a weaker line than true fighters. Undoubtedly, fish like these fought by people indescribeable by any term other than "moron" die if not assisted immediately.