Allegedly they shut off sales because the servers were so overloaded that players zoned in and all but could not move, for the lag. GENIUS!!
Still a very poorly thought out move, but this IS NCStupid we're talking about - so what else would we expect. You don't shut down the kitchen when the hotcakes are flying out the door, that's just stupid.
Except that isn't what happened.
NCsoft forced Anet to release GW2 before they were ready to do so.
It was Anet's decision to shut off sales because their infrastructure was groaning - but at no time was anyone unable to move from lag. Most of the problems had to do with zoning parties into the same instances, overflow servers becoming glitched, and glitched events.
Anet is a great dev team and had repeatedly told us through the long betas that they wouldn't even release hype about systems they didn't have working yet to the general public. Anet's decision to shut down sales is because they actually give a crap about their player's experiences, it was not a decision of NCsoft's.
NCsoft's stupid move was to shove GW2 into a release just to shore up their terrible Q3 numbers.
I'd also like to see a cite on the "expecting 6 million in sales" thing. I hear it thrown around, but as someone who was avidly watching Anet through the beta process, I never saw it. People may be confusing it with the announcement that the GW franchise as a whole sold 6 million units as of April 2009, but I could be wrong, I'd love to see a link.