Storm Raven said:
Power Attack is highly useful against two classes of opponents: (1) high hit point opponents whose AC is low enough that you can take a BAB loss and still reliably hit them, converting the wasted BAB to damage and (2) opponents that you could only hit with a 20 anyway.
If most of the oppents you face fit into those two catagories, you fight a scewed selection of opponents.
Storm Raven said:
No, you are describing Great Cleave. Cleave is useful any time you are facing more than one opponent. At some point, one opponent will fall, and you will get your extra attack. If you are a 10th level fighter facing a crew of 50-60 hit point enemies, you will probably get an extra attack every other round or so. That is a big deal.
Great Cleave is still useful for many high level fighters. They may not be fighting goblins, but there are enough instances where midrange opponents show up that he can drop one or more in a round to make it a very worthwhile investment.
If you are facing 4 enemies, you assume that every time you down one, another will be in range? Think of fighting the iconic party: cleric, fighter, wizard, rogue. Wizard won't be in melee, the cleric would back up and heal himself. Rogue should have the good sense not to get that low on HP. Again, skewed matches.
Storm Raven said:
Using a reach weapon helps a lot when dealing with Combat Reflexes. It makes it really difficult for most enemies to avoid them without conceding you an edge in positioning. Avoiding the AoO from a reach weapon user frequently means that you have to conceed a rounds worth of attacks to him, once again a significant damage potential added. Also, never forget the damage potantial of being able to make AoOs when flat-footed that Combat Reflexes gives you. Many opponents do silly things when they think you are flat-footed.
You must face a lot of stupid opponents. If you have your reach weapon out, they should assume you can use it, or they shouldn't be alive long enough to reach higher levels. 1/2 cover stops AoOs, so think tower shield, or useing the guy in front of you. Many monsters have reach themselves, and don't charge up. Then, what happens if they open combat with twinked out archers of their own? Combat reflexs is nice, but far from increasing your average damage output more than slightly.
Storm Raven said:
And the ability to do something like triple damage reliably once per day is a big deal. Esepcially for a high powered melee fighter who gets a lot of his damage from the added modifiers. A 26 Strength 10th level Fighter with a +3 Glaive and Power Critical sees his damage on his Power Critical attack go from 1d10+17 to 3d10+51, quite a leap in damage output that will skew the results a bit (especially given that most high level combats are over in a handful of rounds). If that allows him to trigger a Cleave, all the better.
[edit] missed the word melee in there.
If you only swing your weapon in combat 10 times in a day, sure you are looking at a big boost. And if you have 5 combats in a day, all lasting 4-8 rounds and you are throwing 2-3 swings per round average, that extra isn't nealy as impressive.
While we are on the subject, archers will get more full attacks anyway, as they don't have to run into melee.
Storm Raven said:
Conversley there isn't a "get a free attack when you drop a n opponent" feat for ranged attacks. Feats frequently make the melee damage output go up. They allow for additional attacks, stronger attacks and so on.
No, they get an extra attack all the time

Feats for general combat abilty, like weapon focus and specialization, also tend to work with ranged weapons. Melee options are, by and large, other options for combat, not better ones.