Is there a particular developer clause that was violated? If so, why is the facility blocked only on the Nexus and not other Android based devices?
I did some digging around and found that this change was introduced in an update for Gingerbread. It applies to all Nexus devices starting from the Nexus S (except the Nexus One since it comes pre-installed with Facebook).
The problem Google has with Facebook sync is the inability to port the data that Facebook sync adds to the contacts, out of your device.
Here is an excerpt from their statement on this issue:
Since Facebook contacts cannot be exported from the device, the appearance of integration created a false sense of data portability. Facebook contact data will continue to appear within the Facebook app. Like all developers on Android, Facebook is free to use the Android contacts API to truly integrate contacts on the device, which would allow users to have more control over their data. We are removing the special-case handling of Facebook contacts on Nexus S and future lead devices.
TechCrunch's coverage on this: http://techcrunch.com/2011/02/22/google-android-facebook-contacts/
I am still trying to find the official statement on a Google site. Will update it here if I find it. Also I want to know why Google doesn't get all manufacturers to enforce this rule if it is part of core Android policies.
According to a post in a Google Product Forum:
A sync between Nexus devices and Facebook isn't possible by default. To get that information on your phone you will need to install a third party application that will sync the information to your phone.
Manufacturers like HTC and Samsung enabled this on their own for the people that bought their devices.
An alternative to make this sync happen is to use a 3rd-party app like Sync.ME - Sync for Facebook:
• Full Screen Caller ID - See your friends' picture from Facebook, LinkedIn or VKontakte when they call you and when you call them.
• Smart Matching - Matches automatically between your contacts to their social network profiles.
• Contact Enrichment - Magically update your contacts with missing details (phone number, email, company, job title, address & website).
• In-Call Experience - Take your phone calls to the next level! View your friend's latest social network posts and photos during call.
• Birthday Reminders - Never forget your friends' birthdays again! Create and share personalized greetings for any occasion.
• ME Card - Your ultimate contact and business card. Choose how you appear in your friends' and colleagues' phones. Edit your picture and details to keep them updated.