The answer is not as easy as your question, and actually neither is your question, depending on how literally it is read or rather between the lines
There are reasons why some distributions work so that they put out a "release" which then gets updates (usually smallish, related to bugs or security) but usually no new big versions of any software---for example the Ubuntu case you mentioned, that they put OpenOffice.org 2 into the 8.10 release and version 3 to the next version. One of the reasons is that it's too much work to try to keep every piece of software bleeding-edge new
and stable (not everything is still solid as rock this way, but more than if everything was updated every day into new versions). Anyway, if you read enough from various sources such as the distribution websites, you finally may agree that this is sane policy, and we can move on to the question of getting really
new things as updates, not just fixes.
Usually a distribution has several reposities (not necessarily, but it may have): for example one for main software packages, one for security-related, one for testing-stage software and so on. Ubuntu for example has several; the one that you may be interested in is called
Ubuntu BackPorts. There are pros and cons with using this reposity (and the others mentioned), so it's up to you to decide if you want to use such reposities; is it worth risking stability to get the newer version, for example?
Then you must remember that there are other ways to get the software than just the few official reposities from the distribution maintainer. There may be semi-official or non-official, perhaps local reposities that contain user-submitted packages for new software that you can use; some may be held by the community and even well tested, but yet not "official" because the actual distribution maintainers aren't officially involved in the thing. Or you can use completely non-official 3rd-party reposities that are known to be "compatible" (again a difficult thing, more a matter of trust than solid science), or you can get the software packaged in a different format (say, as rpm packages for a deb-based system) and convert them some way, or even get the source code and compile it and then turn it into a binary package that you can install. The possibilities are pretty vast.
If you insist on sticking to the official, distribution-maintained reposities, it's ok too. It's a good idea, that way you make pretty sure you don't screw the system up because of non-compatible packages, for example. In the end, if the "backports-style" reposities can't help you out, you can ask yourself why you can't wait for the 6 months for the new version---if the community didn't do it, there's probably a fairly good reason to wait (except for if it's a small, not widely used piece of software you're after, in which case you're easiest off either waiting of compiling it yourself). And in the case of Ubuntu you can check if the older piece of software is somehow patched so you can live with it---for example in the case of OpenOffice, the version 2 that Ubuntu had in 8.10 could work with newer MS Office files that the "original" version 2 couldn't, if I remember correctly (a reason why a lot of people would have wanted to upgrade to the version 3). Thus a big reason to upgrade from OO.org 2 to 3 was worked out not by starting to package and test the whole new version, but by adding functionality to the earlier version, leaving the testing and packaging of the 3rd version to the next distribution release. Most people can live with their current operating system for half a year or even a year anyway, and those who can't usually try something more exotic instead (like LFS).
The question is far from silly. The answer is mostly just that there's not enough time (human or computer) to work out all the updates to everything, probe and test them and make them ready for the end-user every day; if there was, we wouldn't probably be using
N-month/year relese cycles, but instead have our updates served every day.
Remember: it's mostly free of charge. How much can you expect without feeling guilty?
