Live tiles alone had one glaring hole: Miss a toast, miss it forever.
In discussions of "WP needs a NC!" I always saw that people just wanted a clone of android's status bar. I recognized that such a status bar would undermine how important developers considered live tiles to be and the app ecosystem would degrade over time. I recognized that if not implemented intelligently, there would be a significant amount of redundant notifications between the tile and the NC (a problem iOS still has), and using one or the other would result in the accumulation of junk.
My answer to every feature request that ends in "like Android" is usually always "then go buy an Android phone", but something was definitely needed to cover the aforementioned hole in live tiles. I supported the idea of fixing this, but I hoped MS would ignore the consumer desire to just copy Android.
Ideally, only missed toasts would populate the NC (which I proposed could be a tile itself), and it would automatically clear when the appropriate app was launched.
The flexibility of the notification center is elegant, and my idea to force the correct way on all users would obviously have been resented, so I believe they did what was best. They skirted around the data redundancy problem effectively. It just saddens me that it falls to the user to know how to configure it in a coherent way.
The true beauty of live tiles is often unappreciated: Less stress. When your phone beeps, you compulsively check it. You can't ignore it, even when you should be doing something else. This creates a perpetual stress and an actual, measurable addiction to your phone. These aren't monumental issues to be sure, but that doesn't mean they don't negatively affect our lives, and hourly mood.
The passive nature of WP's live tiles helps to discourage this. You see things when you check your phone; only when you happen to pull out your phone will you be presented with information. You aren't a slave to every beep and chirp, you don't feel the need to check your phone the moment something new happens, something which really can wait.
The NC allows this by configuration (silent toasts, don't toast for certain apps which could be using tiles already), but now not every user is automatically benefiting, and many will never realize the benefit they lost.
I won't use the tired and stupid "it's bad because my grandma couldn't use it" argument, I will only speak for myself and the configurability allows for my perfect ideal setup. But the unique image and inherent benefits of WP will take a hit on the whole for the default configuration of this NC.