See, that's what I am talking about. If you give devs the possibility to run something like "give a sound notification every 30 minutes, until the user sees the notification", you are going to end up with an app running in the background waiting for 30 minutes and checking for new notifications. In theory it might work...sure. But the reality (on android) shows us, that there are a lot of risks doing this. In theory an app doing the same just on a visual way should work just fine, right? the reality is: there are users who have no problems with apps like that. But there are also a lot of users having trouble with battery drain or other issues created by apps like that... I am one of them.
And this is just one example for "close system vs. open system". They have both their advantages. I for myself love using close systems because they are a lot more stabile (as I already mentioned: my HTC 7 Pro worked 111 days streight without any issues or whatever. None of my friends trying to do the same with their andorid devices made it to week 4 or 5 without rebooting the device).
WP does not lack thousands of features... i sure needs some! But all in all i am a lot happyier with my WP than I ever was with my old Iphone or all the Android devices I uses for work...
"It would be enough giving developers access to wake-up display function (by explicit confirmation, just like when an app have to use gps or stop the music) and you'd have your silent notification without a LED." I guess you don't know how such things work... it is not that simple and would require background tasks of checking and showing stuff and so on... there is no "simple" way of doing this..