Better security for you makes Apple look better, and looking better with regard to security (a major selling point for the Mac), helps Apple sell more products. Apple doesn't want to encourage you to sit on old versions of the Mac OS, they want you to have the latest and the greatest security measures they can provide. Second, Apple wants to constantly drive you to newer versions of the Mac OS, since they include, not just the latest technology, but much more importantly, they include the latest SECURITY.
I'm sure that they have no desire to try and make new apps work on outdated versions of the Mac OS (which don't contain the latest technology), especially now that they have just given you a new version of the Mac OS FOR FREE that includes the latest technology. For instance, Apple is constantly updating the graphics routines that render complex graphics on your Mac. The first is that each new version of these Apple apps is optimized for the technology that is contained in each new version of the Mac OS. Click to expand.There are a couple of possible reasons why Apple's apps, like Pages and Safari, are tied to the version of the Mac OS you are running.
