And in fact this case is often more the important one. Packages that depend on having a *recent* version of python will often crash quickly, before doing permanent damage, when an undefined syntax, function, or method is invoked, while packages that depend on a quirk in behavior of an older version will typically silently corrupt data.
How can they know that they depend on "a quirk in behaviour of an older version" if a newer version hasn't been released? This sounds bogus.
Besides, not letting me install their app/library on a newer Python just because they are not /sure/ it will work is IMO an active nuisance. The user should be treated as an adult.