In Windows 8 DP has Facebook apps, however it called as "Socialite". But your concept was better rather "Socialite" in Windows 8 DP, it has messages, event, group, apps, feeds, and pages feature which "Socialite" doesn't.
But Microsoft Says that "Socialite" and "Tweet@rama" are only demo apps for the developer preview. I think that in the beta or the RC will be erased and Facebook and Twitter respectibly will make ther apps avalible for download
Maybe... It was transformed to "cebook and Twitter respectly as in Windows Phone. I think the Beta version of Windows 8 was only contains Internet Explorer 10 Metro, PC settings, and Store. Apps can be downloaded separtely in Windows Store.