1. Archer rangers are seemingly intended to be glass cannons.
2. Our group's tests of them indicate that they do FAR more damage than any other build our party has yet tested. It's just not even close.
3. Archer rangers have abilities to avoid melee opponents that no other glass cannon (see: Wizard) enjoys. By level 6, my archer ranger with Weave Through the Fray and Yield Ground can seriously bedevil pursuing attackers while turning them into pincushions with his sheer damage output.
4. Archer rangers have a natural synergy between their DEX for attack and DEX for AC and Reflex that is not enjoyed by dual-wield rangers. In fact, the dual-wield ranger was significantly more difficult to make competitive until I forgot about DEX entirely (set it to 8) and dumped into armor feats instead. Hell, the only attributes an archer ranger even needs are DEX, WIS, and CON (in that order). This conveniently gives them bonuses to all four defensive types as well as bonus hit points and surges. This more than makes up for the lack of the Toughness feat, seeing as they shouldn't even be in melee to start with.
5. Archer rangers can avoid melee VASTLY more easily than laser clerics (range 5), warlocks (range 10) and wizards (range 10). Your -close- range is a multiple of their -max- ranges.
6. I don't know about anyone else... but what chances we've had to test archer rangers, it is indeed very rare to see them in melee combat. Where it has happened, there were ways for them to slip the combat while the tanks used marks and other means to regain the attention of enemies. Hordes of ranged attackers concentrating fire on an archer ranger was vastly more dangerous.
Mind you... they are a bit glass cannon-like. If your archer ranger gets surrounded by big tough melee brutes that your friends can't shake off of you, you're toast.
Now... by contrast...
Melee rangers have, at least in my experience, a much rougher time of things. They typically have less AC (unless you dump DEX and invest in armor feats), less Reflex, are more susceptible to being whacked on in melee when they're so much more attractive as a target than your tanks, and other liabilities.
Maybe there's something I'm missing, but our group's tests of both builds have seemed to indicate that the archers were -vastly- superior.