I agree that "Castle" is a red herring. The iCloud website just announced their new name, "CloudMe." It seems unlikely that a site name change is created unless directed by new management. Also, the url "icloud.com" redirects to "cloudme.com." I'm guessing this is a juxtaposition of 'iCloud' and 'MobileMe'. Such juxtapositions would make sense if a company wanted to retain brand loyalties.
Also, if the updated website is any indication, I'd bet the Apple schema will be 3-tiered:
1. All users-free 3Gb cloud storage with 150MB/file and adverts.
2. $50/yr-25GB, 150MB/file, NO advertisements.
3. $100/yr-100GB, no limits on filesize, no ads.
This way, they avoid the "email for life" fiasco of the earlier .mac, yet retain financial incentive to continue serving cloud services.