We do a check for script updates once per week. And I should note that we aim to have the latest _well tested_ and _stable_ version of the script, not nessessarily the most recently-released version.
But what you're both really talking about here is _upgrading_ of existing installs, which is something on our todo list (and the seeds of such functionality are already in Installatron), but it will only be something we will attempt fully after every other little Installatron feature is working to optimal effect.
There's a reason why no auto-installer to date (that I'm aware of) handles upgrading of installed scripts -- not even Fantastico -- and that's because upgrading is a lot more difficult to support than straight installing.
Straight installing isn't even that easy to do, but upgrading existing installs is far more difficult to support over long term.
Phil and I have talked at length about ways we could do it, and it will be something we take a genuine swing at in the future.