It's because Apple keeps messing with the operating system on iPhones that it doesn't really qualify (and nor does it come with a keyboard)
The C64 had the same BASIC and KERNAL ROMs for the entire production run, meaning that each revision of the hardware was equally 100% compatible with any other C64.
You can't really say that for most computer lines. Take the Atari 8-bit line, the Apple II series, or the Commodore Amigas..... All different revisions of essentially the same computer in different memory, kernel, and language configurations. Oftentimes the different cases prevented certain expansions from working correctly, but not the C64.
Sure there was the C64 breadbin and C64C cases, and yes there were motherboard revisions of the circuitry including some sound and CPU chip revisions which were different yet otherwise 100% compatible... but other than that the Commodore 64 was a consistant platform for it's entire decade-long production run. Perhaps because of that, it held it's own defacto standard to which all demo coders could pitch towards in the demo scene. They weren't shit-fighting over using different hardware chips or memory expansions as the Amiga demoscene had to put up with. Most demos (with some notable exceptions) all used the stock hardware with a 1541 disk drive.... and that was it, and those were the rules that everyone understood (and still understands)
For that reason the demoscene on the C64 has stayed more or less constant too, and hasn't died like the other demo scenes.