Um, Neonivek, a lot of your statements are simply not true. In order:
1) A highly trained bowman has pretty fantastic range. It's difficult to judge Dwarf Fortress ranges, as a square can hold anything from a single seed to a colossus, but I'd say that bow ranges are, if anything, on the short side. The fact that adventurers can't see much beyond their toes is a separate issue.
2) Again, training helps a ton with accuracy. Modern competitive archers can regularly hit a target outdoors at 200 yards, and the extra gadgets and pulleys don't help that much over what a trained longbow user could do.
4) Chainmaille is crappy armor. I know this; I make it. Chainmaille armor was made because Dark Ages smiths lost the technology needed to make high-quality sheets of metal; the metal wire used for chain was much more forgiving. But a high-speed arrow has some serious force behind it and could easily split rings open. Chainmaille is only really useful against slashing attacks, where a sharp sword edge is basically turned into a thwack with a blunt stick. Even then, the rings would become creased and would have to be replaced. As for plate armor, I know less about it, but a high-speed arrow applies a lot of pressure to a very small point, much like a warhammer or battle pick would, and those were the ideal weapons for puncturing plate armor (whereas a foil would be used to slip through the chinks).
5) Skilled bowmen were pretty fast. Again, it's hard to say how quickly time passes in Dwarf Fortress, but an archer standing his ground against a charging foe on a horse had plenty of time to shoot him down. See also the battles of Crécy and Agincourt (and note that the French knights wore armor of chain and plate).
6) There was a Mythbuster's episode about grabbing arrows; suffice it to say it's not gonna happen outside of fantasy. Blocking arrows you know are coming is a good point, though. Assuming you tried to deflect the arrow instead of block it head-on (so to speak), you should be able to defend yourself fairly well, though you wouldn't have much time to attack.
7) Arrows stop at any solid obstacle or creature. This includes hitting trees, though since the arrow has to hit the precise square the tree is in, this is unlikely outside of heavily-forested maps.
As far as overall effectiveness of archery, Dark/Middle Ages archers tore armies to shreds when they were well-trained. There's really not a lot you can do to an enemy who can kill you before you get close, except to hope you get close before he knows you're there (or get close so quickly that he can't kill all of you before you're in melee range). Armor was not universally effective. Look up the meaning of "clothyard shaft" sometime - arrows were big, as big as you could make them while still shooting accurately and with range. While armor did eventually start to have moderate effectiveness against archers, shortly thereafter, archery was replaced by muskets, making armor largely moot anyway. For the time period we're looking at, you shouldn't expect your armor to protect you unless it's actually a solid wall you're hiding behind.