[nightski]

Probably not a good idea to update the framework without the application knowing. This could cause bugs and unspecified behavior. It's best to test your application against new versions and then deploy a new version of the app.

[cm2187]

The .net framework is pretty much always 100% backward compatible. Again not a problem if you will have an active team maintaining the code. But can you even count how many dead applications and websites you have encountered in your career? At least if the OS gets updated, the application benefits from security patches.