No Other App Uses Notification System

For me, the notifications on my desktop only show mails, system notifications and nothing else. No other app uses the notification system, while they could (for example skype, viber, games and so on).The notification system is another failing feature or we hope to be improved?

And secondly is the expand button, where you can press the little arrow and it will show you 50 more characters of the message/mail you got. it is obvious that this doesn't work, if you have used it you know: if it is an email, you want to read it all, or you want to mark it as read, or you want to reply, but you cannot do it through the expand button, so it is useless. On w10m you can answer an SMS from the notification bar after pressing the expand button, which is great! But why not any other app uses that feature? Is the expand button another failing feature or we hope to be improved and used by other apps??