Howdy all,
The Package Updates module has been updated to version 4.3 to address a misbehavior during upgrades of Apache packages on Debian and Ubuntu (I hesitate to call it a bug, as it feels more like poor behavior on the part of apt-get, to me, but Jamie implemented a workaround).
Other operating systems were not effected by this bug and so don't need the update.
The specific problem it addresses is that upgrading Apache packages in the Package Updates module would lead to apt-get removing mod_php, as well as some necessary configuration, and switching to the worker concurrency model, causing PHP to break after the update (and possibly other stuff). Again, this seems bug-like on the part of apt-get to me, but by changing the order of operations in the security-updates module we can avoid the problem, so that's what the new version does.