Why do the start screen Email and SMS tiles number of unread emails count disappear if not read?

[WPCentral Question]

For example, the Email or Message tile number disappear when you open and close the app though you may not have even opened and read the message. iOS and Android keep the number of unread messages on the app icon or tile until they are read.

 

[xandros9]

Its default behavior.
Why? We can only speculate.
my thinking is that is shows what has happened SINCE you last opened the app.

I'd like the option, but that's just how it is.

 

[jmshub]

They treat opening the app as acknowledging the notification. I prefer it that way, to open the app to clear the notification. But I suppose there are some people that would prefer it your way.