Isn't that redundant?
Right now if you receive a toast and miss it, your live tile will show a count. So all you have to do is:
1. scroll down with a flick or two
2. then tap on the live tile.
I don't see how a notification center would save you time?
1. You scroll to your notification center (be it a tile or another screen to the left)
2. you tap on the notification center (if its a tile)
3. then you scroll through all the notifications
4. then tap on the one you want.
Sounds like more work to me.
Because in a Notification Center instead of jumping in and out of apps you see everything on one screen and can discern the importance of all those notifications comparative to their peers and triage them more efficiently and effectively.
Quick Analogy: What you're saying is that when you go into an emergency room, the guy who only has Bronchitis should go ahead of the guy who just got his arm blown off by a shotgun simply becuase the Nurse walked (flicked) past him first. That's not the way these things work. People like being able to easily discern importance and get at the important things first, even if they were not the first things to appear on their screen.
You're being a bit intellectually dishonest in how you describe it. You forgot the part where you tap on the Live Tile, then have to Swipe left (Me Hub) and then Click on the Notification to actually see it, and even then there is information missing there that you'd get in the full app. The FB app may or may not load your notifications properly, but it takes as many steps. Lots of apps are lick this. Weather apps send you toasts but if you miss it you have to click on the tile and in some cases click on another link inside the app to get to that (or swipe to it). That's unnecessary with a notification center becuase that Notification persists there and tapping or swiping it deep links you straight to the relevant data - it's at least twice as fast because on some devices (i.e. iOS 5) you can do this from the lock screen. Live Tiles (99% of them) don't or can't do that.
That means when you get an SMS you click that Notification in the Cache and it takes you to that conversation, not the conversation LIST like opening up the Messages Live Tile on WP7 (you may have to swipe just to get to the flick conversation if you've had multiple incoming messages, but with previews in Android/iOS you can get to the more important messages much quicker right from your Notification cache).
There's nothing faster about Live Tiles (which are as useless as Badges) compared to a Notification Center. The latter is clearly superior design and clearly more efficient and effective in triaging Notifications and getting to the relevant data faster.
And on iOS you can even tell it how to organize your notifications in the Notification Center, giving it even that extra bit of efficiency to go along with an obviously superior design. That way, for example, a Facebook Notification will never show up in Notification center above a Missed Call, SMS, or Voice mail (example, but easily doable just by arranging them visually in the settings).
Live Tiles = Badges with some Widget Functionality. They aren't innovative. They aren't anything new that could not be done on an Android FroYo device (updating Widgets via Push Notifications, etc.). They aren't even half of what a good Notification system should be composed of.
Additionally, there are technical issues that plague the Notification System in WP7. Their PUSH servers routinely act as if they're overloaded. Push Notifications on WP7 are always slower than on Android and iOS (I've already put multiple videos on YouTube to display this - they're gone since I no longer have a Google Account, though). BB is faster than all of them, very easily...
Lots of Live Tiles are updated with Background Agents which make them fundamentally useless from a Notification point of view (but somewhat useful aesthetically since you could still argue they're live). It might become current in 30 seconds. It might become current in 28 minutes. This makes i.e. the Me Hub Live Tile pretty useless since it cannot be depended upon to deliver the notifications in what anyone would consider is an acceptable "average" time.
Microsoft isn't consistent in how it implemented Notifications across its own Stock Apps. Messages gives toasts. Great. eMail doesn't so you never know if it's a Newsletter or an important email unless you unlock your phone, open the Hub, and see for yourself. Obviously no Toasts for Social Stuff. You don't even get a ringtone for those : Yay.
The Notification system is half implemented, the PUSH servers are underperforming (Facebook Notifications are almost always 5-10 minutes behind iOS and Android, even when I tether my iTouch via my HD7 it outperforms WP7 push notifications by that much), and they aren't even consistently implemented across Microsoft's own stock apps.
There is a lot of work for them to do when it comes to that.
Doubt they care about those feedback threads. Numbers on blocks seems good enough for them, even though it causes you to do 3x the work to clear your notifications as on other platforms.