They probably dropped the prototype and had to reschedule. Also why reveal in May if E3 is around the corner? Hmm..
They've recently switched to doing Apple style keynotes at their own venue/time/location/etc. This way they can get ALL the hype and media for themselves and not be competing with the rest of the expo floor. This is going to become more and more standard for the tech industry. (Apple, Google, Samsung, and MS already do it).