When you own something, you can run it forever, even if the developer decides to stop using it.
In theory, yes you can keep using unsupported software. The reality is that most companies would ultimately be better off if they were forced to drop it sooner rather than later. It hurts to rip off that bandaid, but it's usually worth it.
It doesn't give anyone anything.
If you happen to be selling insurance, it gives you quite a bit!
1.79 x 10^12 furlongs per fortnight -- it's not just a good idea, it's the law!