It's important to fully understand the mentality behind the 6 month release cycle, once you do it makes perfect sense.
There are many benefits to the 6 month release cycle. But in general, these restrictions are in place to serve as a commitment to quality, and to keep the project goal oriented. Now as I was saying about the mentality behind the decisions. As the Ubuntu website says:
As an analogy, consider a play being produced in a theatre. While things may go wrong during production, even (perhaps especially) on the night, tickets have been sold and there is a very high cost to backing out: "the show must go on".
A roughly 6-month release cycle allows them to coordinate development of the features that have actually been implemented, allowing them to maintain the quality of the overall release without delaying everything because of one or two features. Updates to programs and projects come out constantly, if they kept on waiting to implement features, we would never see a new Ubuntu release. Setting a specific date insures that they plan responsibly.
The 6 month limit was chosen because that is the release cycle the Gnome project uses. Gnome is what Ubuntu is built on, so naturally they follow their release cycle: https://live.gnome.org/ReleasePlanning/TimeBased
You can read all about it on their Wiki, it is a VERY interesting read and helps one understand it all, read HERE.
Ubuntu releases are challenging because they represent an aggregation of the work of thousands of independent software projects. We feel that a time-based release process enables us to provide our users with the best balance of the latest software, tight integration, and excellent overall quality. - Ubuntu Wiki
In conclusion, keep in mind that there are projects that are planned to be completed over multiple releases. Not everything is a 6 month affair. Also, if you stick to LTS release, you will get a more solid and bug free experience. A lot of people only use LTS, meaning it's more of a 2 year release cycle. From 8.04 to 10.04, and from 10.04 to 12.04, there were massive differences.