Why didn't installing Blender 2.82 delete 2.80? Installing version 2.82 did not automatically delete version 2.8. Is it standard for a new version of Blender to not delete the previous version in the installation process?
It varies with the OS and the method of installation (archive, repository, installer...).

It's totally fine to have two (or many more) different versions installed, that shouldn't cause any issue. Of course, feel free to manually uninstall the version you don't need anymore.