I guess it's good you've got a solution that works then !
If you had the option the simplest way to poll for changes would be to do a hourly/daily/weekly zone-transfer. But many DNS-hosts disable those for security reasons.
Yeah thats the trouble. The big providers disable zone transfers so you have to hope for an API. A lot of providers don't make one available. Besides the ones I have up there, there are only 2-3 more that provide a workable API which I'm planning on integrating soon (Dyn & Azure).
If you had the option the simplest way to poll for changes would be to do a hourly/daily/weekly zone-transfer. But many DNS-hosts disable those for security reasons.