And android 4.3 is bringing users unified game-centre and passbook features because no other OS innovates like Android....
Oh wait..
They all refine, copy, remix, enhance features. What does it matter who did what first as long as the consumer keeps getting a better experience year upon year irrespective of what OS you are on.
nah mate, 4.3 doesn't include those, that was Google I/O releases, 4.3 isn't released yet, the GameCenter, is not GameCenter as such, as I used to have an iPhone, game center was more social, etc. But Google Play Games service is more like a PSN, XBOX LIVE, or Steam, based for more gaming less socialising. Google is heading up to their "console" I think, and so they need this, and they are trying for a "gaming android world", which things like OUYA has started Passbook? Yes you can have that one
But that is only 1 thing, in a world of things going the other way.
TL;DR Google Play Games is more like PSN, than a social gaming like GameCenter, heading up to Google Console. Passbook, yes, but many other things are in the other direction.
As for the question. I believed iOS has bloody caught up, Google has not released 4.3 at I/O setting them 4 months back, but that won't hinder them as iOS7 will release at the same time. But leaks suggest 4.3 should be more like 4.2.x as it is nothing big enough to even deserve a 4.x update, BUT maybe some big things haven't leaked. Plus I believe a 4.x update will hinder them, forget it, make us wait 8 months instead of 4, skip 4.3, go to 5.0, to maintain that "lead" on iOS you can't just give us a bloody bluetooth update, I mean WTF? Do many people use Bluetooth, apart from headsets and controllers anymore???
TL;DR Google, drop 4.3, go 5.0, iOS has caught up, we can wait some extra time, you already made us wait anyway.