Apple has apparently decided to kill support for OS X Snow Leopard, the 2009 operating system that has resisted retirement for more than a year.

On Monday, Apple did not update Safari 5.1 when it patched the later Safari 6 and 7 for newer editions of OS X, including 2011's Lion, 2012's Mountain Lion and this year's Mavericks.

Safari 5.1, which was last updated in September to version 5.1.10, is the most-current Apple browser for Snow Leopard.

Historically, Apple has patched Safari longer than the supporting operating system, so when the Cupertino, Calif. company calls its quits for the browser, it's already decided to retire the pertinent OS.

In July 2011, for example, Apple patched Safari 5.0 for the final time, updating the browser to version 5.0.6. That edition was the last that ran in OS X Leopard, which was released in October 2007.

Apple provided the final update to Leopard in June 2011.

The company did the same for OS X Tiger, officially known as OS X 10.4, which was retired from support in September 2009, more than four years after its introduction. Apple continued to update Safari 4, the newest version that ran on Tiger, for an additional 13 months, last fixing flaws in the browser in November 2010.

Snow Leopard was last updated with security fixes in September, the same day Apple last provided the final patches for Safari 5.1.

Traditionally, Apple has patched only the OS X editions designated as "n" and "n-1" -- where "n" is the newest available -- and discarded support for "n-2" either before the launch of "n" or immediately after. Under that plan, Snow Leopard was "n-2" when Mountain Lion shipped in mid-2012, and by rights should have been retired around then.

It wasn't.

None of this would be noteworthy if Apple, like Microsoft, clearly spelled out its operating system support policies. But Apple doesn't, leaving users guessing about when their current Macs will drop into the unsupported dustbin.

"Let's face it, Apple doesn't go out of their way to ensure users are aware when products are going end of life," said Andrew Storms, director of DevOps at San Francisco-based CloudPassage, in an interview. "They live by the motto that users will just take all updates all the time as soon as they become available. Or users who are left in the dust will just go to the store and buy a new device."

The causes of Apple's longer-than-usual support for Snow Leopard are just as opaque -- Apple habitually declines to comment about anything related to security -- but analysts and experts have tapped several reasons.

One is Apple's accelerated release schedule, which now promises annual upgrades. The shorter span between editions means that unless Apple extended its usual support lifecycle, Snow Leopard would have fallen off the list less than three years after its launch.