You're quite right when you say I don't know much about Macs. I have no idea what is the current rev of OS X, so Yosemite and El Capitan are just noise to me. The point here is that my friend's Mac apparently couldn't be upgraded to run a compatible version of the Airport Utility in order to manage her new Airport Extreme, which is absurd. Were the Airport Extreme to have a web based management interface, like EVERY OTHER consumer router on the planet, her old Mac, as well as any other machine with a web browser, could have managed it.
As for running Linux on old hardware, it's not just that it runs. It's *USEFUL* too on old hardware.
As for the CLI to manage the Airport Extreme, what makes you think that rev of the CLI would work if the Airport Utility wouldn't? The GUI is just a front-end to the CLI.
The point here is that Apple's gear isn't compatible with itself over time, and it forces people to purchase upgrades unnecessarily. I suppose the best thing you could say for it is that its clearly a successful business model...
All very well, but it comes off as baseless Apple bashing - you admit yourself that you don't know anything about it. The Airport Extreme is controlled by an application and always has been, and the system requirements are listed on the box. Your original comment posited an impossible situation - I can't think of any combination of Apple laptop hardware and AE hardware that would result in incompatibility if the time is restricted to 4 years.
Sure the choice of using an app to control the AE is an unusual one, but it works on Windows, OS X and iOS and it works on pretty much everything.
My thought is that you have fudged the numbers a little to make it sound worse than it is. The 6th Gen Extreme (that requires Lion to set up on OS X) was released in 2013 and the last Mac laptop that can't run that was released in early 2006 which is 7 years, since it came out in June 2013.
If it's any AE earlier than the 6th gen then the software will run on any Mac released in the last 13 years (going back to the PowerPC G4 era).
If you're going to tell tall tales, you might not want to tell them about things that (you personally have admitted) you know nothing about.
But what am I saying? I'm interrupting an anti-Apple circle jerk. My apologies, carry on.