Nintendo is so smalltime that they had no choice but to reveal those first party exclusives to keep their system alive, Sony can afford a few surprises here and there.
Remember, Nintendo had stockholders backing-out around this time last year.
They may be "smalltime" but at the very least they announced some promising titles people actually care about. It also doesn´t make much sense holding back if your system is selling as bad as Vita right now, especially "Vita Heaven" (obviously they felt the need to react due to their lackluster performance) lead some people into thinking they actually don´t have much up their sleeve. That´s not exactly a very brilliant way to establish a new system.