10 years ago is giving Apple too much credit. They were using Intel processors then, ARM now. For now, you can still run Intel applications, but that won’t last much longer.

More importantly, a 10 year old application is likely to use Carbon instead of Cocoa. Unless it’s an extremely simple application (i.e. hello world), it is unlikely to run.

Then there’s the depreciation of resource forks, a new filesystem, tons and tons of extra security restrictions, etc.