Hi Rafael,
think of dot releases as a kind of service pack. It's a sliding update. Once 6.4 is out, all fixes go into 6.4 and not 6.3 any more. There are very few reasons to stick to 6.3 once the next dot release is out.
The same is actually true for windows. Once a service pack is out, you won't get updates for the OS without that SP applied.
Greetings, Thomas