Adam Powell, an Android engineer:
In Android 4.0, Holo is different. We’ve made the inclusion of the unmodified Holo theme family a compatibility requirement for devices running Android 4.0 and forward. If the device has Android Market it will have the Holo themes as they were originally designed.
This is interesting. Google and Apple have different approaches to platform building. Google gradually lays down more rules and control over time, forcing the developers and experience more in line every release if they want to be part of the Google platform at large. Apple starts stringent, sees what people clamor for, what they think they can allow without overwhelming the user experience, and then slowly adding features bit by bit.
It's very much a choice between letting the genie out of the bottle and gradually forcing him back in versus letting him out just a little bit at a time. I'm under the impression the latter (Apple) is the far easier and smoother approach to putting the perceived user experience first, while the former (Google) gives developers more of what they demand. I don't think that point is arguable. What is arguable is which one actually ends up building a more fruitful (or, to use an opinion word, better) platform. My opnion is that the Android vs iOS battle has thus far pointed toward's Apple's approach being better for building a real platform--both for the developers who want to make money and the users who want a stable and consistent experience.
Still, even if you'd agree with me on this point (which you might not), this is but one platform battle. We've had others before, and we'll have others again.
What is inarguable is this: Google is improving the experience of Android by forcing authorized Apps to include support for their theme. Therefore, Google is improving the experience of Android by requiring developers to do work they might not want to do because Google deems it better for the user.