We could get upgraded packages for the case that the installed image is old enough, dependencies need to be upgraded to install the package and current package versions are newer than the version of the installed image.
Of course there are exceptions to the general rule where package upgrades make sense.
This is included in the warning recommendation:
Blindly upgrading packages (manually or via script) can lead you into all sorts of trouble.
Just because there is an updated version of a given package does not mean it should be installed or that it will function properly. Inform yourself before doing any upgrades to determine if it is safe to upgrade. Avoid upgrading core packages.
Cases could exist where package upgrades make sense. This still does not mean that the general rule should be dropped to recommend against blindly upgrading core packages.