Since when were the rules perfect? We've had a lot of errata be released thus far, and although sometimes the errata fixes problems, the errata far more often creates more problems. (For example, forcing XP costs for spells needed in item creation FOR EVERY DAY OF THE CREATION is inane and ridiculous because it makes several items IMPOSSIBLE to create, primarily a Ring of Three Wishes, Manuals that give you inherent bonuses, or anything that requires a spell with an XP component of more than 1,000 XP. Think about it. If you change the rule to force the XP costs to be paid, the Ring of Three Wishes takes 500,000 XP to create rather than 15,000. Another good example of bad judging is lowering the threat range of the bladed gauntlet as well as lowering the damage of the mercurial greatsword.) Because of that, I not only ignore most errata as being utterly senseless, but I also house rule anything I deem to be too vague or unaccounted for in the original rules, such as this Whirlwind Attack question.
I consider Whirlwind Attack to be a controlled "spin" attack, and therefore there is no 5-ft. step allowed. Perhaps that is not what the "letter" of the rules states, but I am POSITIVE that it is what the "spirit" of the rules intend. If you don't believe me, ask Skip Wiliams. I know he has a poor track record as far as clarifications and errata goes, but I think he'd call this one the same as I have. There was even a point where I almost rules that Whirlwind Attack hits EVERYTHING within five feet, INCLUDING ALLIES. I figured that such a ruling would be a bad idea, however, and dropped it.
I would suggest going with my interpretation of Whirlwind Attack, and then creating a new feat called Improved Whirlwind Attack.
Improved Whirlwind Attack
You can become an armed tornado capable of tearing up the battlefield.
Prerequisites: Int 13+, Expertise, Dex 13+, Dodge, Mobility, base attack bonus +11 or higher, Spring Attack, Whirlwind Attack, Str 13+, Power Attack, Cleave, Great Cleave, Tumble 6 ranks.
Benefit: As Whirlwind Attack, except you are allowed to move up to 20 feet during the attack, and all allies and foes within 5 feet are attacked. All attacks are made at your full base attack bonus.
