There are possible reasons for this decision. YBCA might be occupied on the date mentioned, or this could be idea of Tim Cook since this is the first time that he will announcing an apple gadget as the CEO of the company. But nothing is clear on what is the reason about the decision of changing place.
Hosting the event at their own place, will give them the flexibility on announcing the apple event.
But of course there is no official news about the date and place of iPhone 5 announcement, all are rumors.
{ via AllThingsD’s John Paczkowski }