If you are running the OS X Yosemite 10.10.4 or earlier by browsing the internet at Safari 10.1.1 or earlier, and come across an error message when trying to access the Apple Online Store, don't be alarmed.
As noted by Macotakara, Apple is for some reason restricting access to its online stores around the world to newer versions of its systems and browser. When attempting to access any Apple Online Store on a system / browser equal to or less than the above, you will only encounter a warning that that OS / browser version is not supported by the page.
Apple's limitations go beyond: If you're on OS X Yosemite using any browser other than Safari, stumbling across the door like Apple's online store doesn't even load in recent versions of Chrome or Firefox, for example. example.
There is no official Apple justification for the attitude, but common sense points to one reason: safety. Older systems, after all, are inevitably more vulnerable to attack and hacking, and keeping online stores the size of Apple on such a large number of systems and browsers could put their integrity at risk; In addition, by imposing this requirement, Ma takes another step to encourage its customers to always upgrade to the latest version of their software.
Now you already know, so.