Google has released the new Android v2.3 (Gingerbread). One of the updates is a new user interface (UI) - which seems to use more blacks. There are reports that this is so intentionally to take advantage of AMOLED displays (who consume no power on black pixels).
Google Nexus-S
This is not really surprising. It seems that AMOLED is slowly taking over the high-end smartphone market (and Google themselves chose an AMOLED for the Nexus-S phone. Or at least in some versions). Come July 2011, when Samsung's new Gen-5.5 plant (with 10X the capacity of their current plant) begins to produce AMOLEDs - and we're sure to see much more Android phones with AMOLEDs.
When Microsoft designed the UI for WP7, they also assumed that most phones will use AMOLEDs and also chose black backgrounds.
