I think you're misunderstanding what people want from a WP notification center. We don't want more updates... we basically just want a list of all the toasts that are already happening.
So when you miss a toast you can go back and see what it was. If you don't care about missed toasts you can ignore it completely... but some of us want to know what that chime was that we missed, and live tiles often can't tell you... especially if the app is not pinned.
It still sounds like something that doesn't require an actual notification center. I guess since I don't use every social network on the planet, I don't know to what extent which application use toast notifications (I also think that term is kind of dumb, but that's irrelevant). To me, when I think of potentially-missed notification, I think of:
1. Text messages
2. Instant Messages
3. Game messages (such as alerts to your turn, game invites, and friend requests)
I think all of these can be handled easily without a notification center that will just add a bit of weight to the OS that I don't really want. For the first, we already have it covered. If you miss a message, it will be on your lock screen. For the second, I have IM+ pinned to my start screen, so the live tile (usually) updates that. As I said, USUALLY, so they need to perfect the live tile updating on that app. For the third, there are two possible solutions. The first option is to give the Games hub a notification center. You can go in, and one of the tabs would be "notifications," where it will list which games have notifications and how many. The alternative (or, perhaps, an extension of this) would be the same as how live tiles currently operate. You give it a number in a bubble on the live tile to let you know that you have notifications within your games. Ideally, this is a Games hub notification center extension. Otherwise, you would either have the Games hub highlight titles with notifications, or you'd do the same number-in-a-bubble notification manner for each game. The highlighting would be more obvious and less clutter-filled, in my opinion.
My whole thing, though, is just that I don't see myself needing a notification center. I don't see any examples where one is REALLY necessary, even. I mean, we have live tiles to cover this for a reason, and if you don't want to use the live tiles for that purpose, I'm a little bit confused as to why you're on this platform in the first place, because that's kind of their staple feature.
I guess I'm not so much AGAINST a notification center as confused as to why people react like Windows Phone is crippled by its non-existence on the platform. It could provide a small level of convenience, but I'm not the least bit concerned with it. I think it's something outside of the top-10 of needed improvements to the OS.