My understanding is that the excessive (and yes, they are stupidly excessive) ambush frequencies were just the result of a bug.
I can understand the desire for more challenge, but the fact is that bandit ambushes are not meant to be the main focus of the game. Eventually the world will have more stuff to do in it, and when that happens it should actually be possible to walk from one town to another without encountering five or six repetitive bandit ambushes along the way.
It also, as others have said, doesn't make any sense for bandits to ambush people away from major trade routes, and makes absolutely
no sense at all for them to charge forward in murder/suicide rushes against armed travelers who show no signs of carrying any valuable goods.
Real-world bandits worked on logical risk/reward. They're not going to attack a pair of guys with swords unless there's a clear way to make money out of it; they're going to focus on less-defended caravans. And if they do attack, they'll demand money, first, which is one of the major problems right now -- bandits currently seem to inexplicably decide to murder you for no reason.
It's also important that any attackers in adventurer mode come from a logical source. That is to say: You should eventually be able to kill all the bandits in an area and pacify it. Infinite random encounters from nowhere is the kind of thing you get in Final Fantasy, not in a believable setting like Dwarf Fortress' world.
DF's world is not safe. There are scary things hunting you at every turn, and entire regions of the map that will reanimate the dead. I don't think a few kobolds and bandits every dozen or so miles is out of the question.
It is absolutely and totally out of the question. Here's why:
1. Dwarf Fortresses' world is meant to be realistic. It doesn't exist specifically to challenge the player any more than it exists specifically to reward the player. It's meant to realistically model a fantasy universe. The challenges it presents should come from realistic sources (wars and
believable bandit predation and magical threats with a clear and specific source), not D&D- or Final-Fantasy-style random encounters your DM pulls out of nowhere constantly just to threaten you. There are
not scary things hunting you at every turn, because there isn't, really, any practical reason for scary things to hunt you at every turn. There are places where there are scary things, yes. But they don't cover the entire world. This is a fantasy game, not purely a horror game.
2. The player isn't meant to be special. That is: If scary things hunt the player at every turn, they should also hunt
everyone else at every turn. And the game clearly doesn't hunt NPCs with the ferocity that PCs (and groups containing PCs) were hunted using the bugged ambush frequency. If they were, nobody would ever trade between towns. Travel is dangerous, yes, but it's clearly presented as a manageable danger -- if you travel in a decently-sized group, you're reasonably safe, at least safe enough to make a profit by carrying good from place to place without an insane risk to your life. Merchant caravans make it safely to your dwarven fortress year after year; they clearly do not encounter the insane level of threat that the recent bugs were causing.
3. Aside from all this, the game should also succeed as a game, and while that means presenting some challenge it also means presenting some interesting goals. The most challenging parts of the game should be in pursuing those games -- that is, it should form an interesting story. Part of the reason why these random Final Fantasy style encounters that some people in this thread seem to like are so bad is because they don't form an interesting story. The game should encourage players to recruit followers and hunt down monsters and explore lost tombs; and if they're busy with generic random "suddenly, 1d6 kobolds attack!" random encounters straight off the D&D random encounter table every five steps, they're not going to get to do that.