Again, i point to my earlier post.

Selling/buying a game:
With the potential of getting your copy signed
Getting the game 2 weeks earlier than retail regardless
Potential to sell early/signed copy on ebay
Very limited number of copies sold "each day" to attendees who would mostly be one-day visitors each day

All very real reasons why the sales performance is in no way indicative of retail performance post launch.

It's like saying a book is going to be a best seller because all the copies at a book signing event sell out, which if you take a look at the real world is rarely ever the case, i had a book signed by david attenborough, its an amazing book, written by a remarkable person, and it didnt even reach the top 50 in UK let alone worldwide, when it hit retail, despite every single copy at the signing event selling out.

I didn`t imply it would be a best seller or anything like that.
If you read my last sentence you`ll see that i separated what happened at PAX from the actual market.

About your reasons, they are basically guesses. Not everyone cares about getting them signed, sell them, then, on ebay. Just because they sold out every day doesn`t mean the purchase wasn`t made by more than one day visitors. The limited number is, as i understand, more of a logistic issue, seeing as the stand selling them also sold other games. Which could lead to people having to wait for another day to buy a copy.
What i can say is that there was demand for the game, signed copy or not.