It's not just the processors that were upgraded in the systems Apple is referring to. Many of them feature a newer WiFi adapter which enables some media streaming and dual streaming features. It's entirely possible some of those WiFi enhancements are required for the streaming to work.
To answer the OP's question, Apple has many ways of knowing which hardware it's OS is running on. It could merely check the driver version for the WiFi adapter or the Kernel's proc id functions.