All the .1, .2 ... upgrades are free downloads. 11.4 is a Lion specific bug fix. If you are using Snow Leopard, you won't get any benefits from this bug fix release.
Thanks. So let's say I buy FileMaker Pro 11.3 now, then delay buying the Lion OS system until FileMaker could be as far along as 11.6, would I be able to upgrade my 11.3 directly to something like 11.6 without doing all the separate upgrades between?
There's no way to know. The latest downloads are available from the downloads link at the top of this screen so you can download and install them as they appear. While FileMaker techs try to make the bug fix upgrades cumulative so that you don't have to do each one in succession, there's no way to guarantee that for the future.
BTW, going by past history, more than 3 or 4 bug fix releases is very rare.