Apple frequently saves its newest features for the latest versions of its hardware and software, though a notice on a preference pane from an older version of Mac OS X suggests the company could be adding functionality from its upcoming iCloud service to the previous version of its operating system as part of a future software update.
Macrumors today posted a purported screenshot of the .Mac settings screen from Tiger (the OS before Snow Leopard and Leopard) noting that it's no longer able to sync up to Apple's servers because the account itself has been upgraded to iCloud.
.Mac, of course, is the precursor to MobileMe, which is being replaced by iCloud next year. Such a message does not appear when attempting to sign in to a .Mac account in Leopard, CNET found.
The message on the Tiger .Mac preference pane reads:
You will no longer be able to sync with this machine because you've upgraded to iCloud.
iCloud requires a computer running Mac OS X Snow Leopard v10.6.9 or later for Contacts, Calendars, and Bookmarks.
The obvious interesting tidbit there is that 10.6.9 has not been released or announced, with the most recent Snow Leopard, version 10.6.8, having been released in June, roughly a month before Lion.
An Apple spokeswoman declined to comment on the matter.
As noted by Macrumors, the system requirements for iCloud so far have only pointed out that "some features" will require OS X Lion, without making mention that others may work on previous versions of the software. In its official press release about iCloud, the company noted that Lion and a valid Apple ID were needed to sign up for iCloud.
Apple has said it will roll out iCloud to everyone this fall. Developers have had the last two and a half months to integrate their applications with the service and the past month to test out Apple's iCloud.com.