This is False, I have seen some bug updates from apple (Fixed the "50 place" Leader board bug). Just like the App store and iTunes on the iphone it is web hosted so Apple can update the app at any time. Thanks
Nop The iBook app is updated on your updates page because you got it on the appstore. GameCenter is web based just like Itunes and apple are capable of changing stuff on it when ever they want without telling you, meaning you wont know that they have done something until you go on the Game Center app.
Personally I think the GC app looks like crap. I was expecting something that looked a little higher quality. In terms of looks, I think Plus+ looks the best, eventhough everyone seems to hate it and it does lag.
oh pity, that not that good. perhabs we will see a minor update regarding GC in next few weeks since its pretty weak compared to OF. BUT I really like the button "play" and you are right in the game, cool idea!