This will (hopefully) be my last response in this debate because everyone here is obviously set in their own opinion. If someone would like to email the Sage on the matter, please do. I tried once many weeks ago, but received no response.
Getting back to the topic, perhaps the real crux of the problem I have with your interpretation revolves around the phrase within 5'. If you want to go by a strict literal interpretation of the feat, things get 'sloppy' (see my earlier comments).
Lets say you're surrounded by four opponents:
OOOMO
MOXMO
OOOMO
O = Open Square
M = Monster/Enemy
X = Character with Whirlwind Attack
Now the character performs a whirlwind attack. We'll say his BAB is +15, giving him 3 attacks at +15 (discounting other modifiers).
Obviously he can hit any of the creatures within 5'.
Now lets assume you can take a 5' step:
OOOMO
MXOMO
OOOMO
After taking two swipes at nearby creatures, he has entered the square to his left. Is he allowed to swing at the creature now at his immediate left, or does he forfeit his last attack because there are no longer any valid targets? After all, the creature wasn't within 5' when he started his Whirlwind Attack, it was within 10'. Technically, it should not be allowed given a strict reading of the Whirlwind Attack feat, though with a full attack action it would normally be legal.
Of course, I don't think you can even take a 5' step at all until after all the attacks are completled.
Basically, if anything, the feat needs clarification, not errata. The description in the PHB isn't incorrect, it's merely somewhat vague. When scrutinizing rules, besides considering designer intent, I try to follow the KISS philosophy. Overanalyzing rules often leads to confusion, and confusion often leads to misinterpretation. In my book, the 5' steps throws a big wrench in simplicity, so that immediately sets off my alarm.
I do understand your position, and I understand your reasoning. However, I don't agree with it.
Of course, I could be wrong, and I'll graciously concede the point should Skip's clarification go against my own interpretation. However, in the meantime, please don't try to stand on high ground maintaining, "I am right and if the Sage says otherwise he is either wrong or it's errata." That's just silly, IMO.