Why don't more apps notify with the light on top?

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http://forums.androidcentral.com – The Note 2 Yahoo! mail app is able to notify you of an incoming email by flashing a light on top the device and not just by displaying an icon on the notify bar. The Treo 650-700 series calendar event alarm flashed a similar light and the whole setup was very useful. With the Treo calendar if an event alarm was set, once the alarm sound or vibrate triggered, you could turn off the sound or vibrate the event, but a light at top of the device would continue to flash until you dealt with event in such a way that the light turned off. That way even if the event's initial sound or vibrate alarm w (HowTos)