What happened at previous NYCCs?
I think previous NYCC's have been ok, but LEGO is newer to the NYCC, as they've only been there with any real presence for the past two years, and they haven't been as crazy with the giveaways.
The problems have been at the last two SDCC's, and the poor planning by TLG in regards to their booth and giveaways. Two years in a row the SDCC admin have had to shut down the LEGO booth due to security and fire marshall concerns. There has been talk about not allowing LEGO to return to SDCC next year unless they can guarantee some real change about how they are doing things.
NYCC admins are just being proactive, and protecting their 'Con from falling into the chaos that SDCC has had to endure.