|No, that is not true. Any application that uses netframworks was written with a certain version in mind. Unless the application was somehow updated to use a different version then it needs the version it was written for until the cows come home.|
Netframework is not like other Microsoft files in that a newer version replaces the older version.
It is possible for you to need all netframework versions.
The only exception to this is the minor updates like netframwork 1 to 1.1. In that case Microsoft will indicate at their update site what the requirements are.
So, you can and should re-install netframework 1.1 if you still have an application that requires it.