I'm not sure backwards compatibility is necessarily the main issue - I agree web apps built 15 years ago are reasonably likely to still function today but user

I'm not sure backwards compatibility is necessarily the main issue - I agree web apps built 15 years ago are reasonably likely to still function today but user expectations have changed a lot and they will feel like apps that are anachronistic. Plus there are often issues with using older SSL protocols , certs signed by no-longer trusted root CAs, and of choose anything using Flash or ActiveX controls etc. is almost certainly now broken beyond repair. The other difference is that users expect web apps to keep working using a variety of browsers (that are constantly evolving) and the backend hosting side posts presents challenges in terms of keeping it running in the face of changing hosting providers, security and availability concerns, cost etc. etc. On that basis I'd agree a desktop app built now is far more likely to still be working as expected with zero maintenance in 15 years time than a web-based one.