Google recently made an interesting announcement on their developer blog. Going forward, all Android 4.0 devices that have access to Android Market will be required to keep the Holo theme Google implemented in honeycomb, and further refined in Ice Cream Sandwich. The goal of this requirement is to create a more uniform feel amongst apps designed for future Android devices.
This does not mean that Android skins such as Sense, TouchWiz and Motoblur are dead. It simply means that certain aspect of the UI must remain true to Google’s original design. Overall, this seems like a smart move on Google’s part, especially considering how much work clearly went into the design language for Android 4.0. This requirement will make it so manufacturers such as HTC and Samsung still have flexibility to tweak Android as they see fit, but at least a portion of the core experience will remain constant amongst all Android 4.0 devices.
Source: Android Developers Blog