Well, archer rangers do have one big benefit, they will be at range and not in melee. This is not listed as a class power, but it's something to think about. They can move around and shoot, climb somewhere to get perma combat advantage for a fight, and not get wailed on by all the monkeys near the paladin. TWF rangers may have an advantage in the overall dps section, at least in herioc tier, but its on average a difference of 1 point of damage. I think staying at range and living longer to dish out the hurt is more effective.
TWF rangers got toughness cuz they're gonna need it. The are prime targets when they get in melee, lower AC then the defenders and a big source of hurt for the bad guys. Who do you think they are gonna go after? I guess on paper it looks unfair, but once again, I find things go well when actually played.
**Edit** Also, archers only need 1 magic weapon and they are good to go. TWF Rangers are unlikely to have a matched set so half of their attacks are not going to be as accurate/damaging as the others.
This. Defensive mobility can be HUGE, depending on the DM. The builds are also very different. The hand-to-hand ranger is not going to max out DEX. The archer is generally much harder to hit than the melee ranger. Defensive Mobility can give the archer a truly impressive AC when scooting around.