As the other thread explains, having a macro like:

/castsequence Nuke1, Nuke2, Nuke3
/cast Purge

.. will actually attempt to purge the target pretty regularly. The problem is that the reason it works is the same reason why a plain /castsequence does bad things to your dps. The above macro will attempt to purge in the dead time between the nukes in the cast sequence. While this makes for nice lazy purging, having those dead periods between your nukes is pretty bad news for your dps.