Also don't forget that at these times we have an influx of new users / users who haven't been around awhile. Which means they all have to download the update all at the same time. If something goes wrong then someone has to try and help everyone out at once, instead of being able to deal with it one person at a time.
And yes, 1.3.4 is a good example, it was rushed out the door, and then a quick fix had to be made in order for everyone to be able to use it.
There are a couple other good reasons why updates can't wait (or be rushed for) the next 'reunion'. First of all, the reunion / whatever itself kinda overshadows any updates to projects that might get released at the same time. It also tends to overwhelm the users who are having to worry about downloading all the different updates. Finally, it makes it easy to introduce problems when an update has to be rushed (or on the opposite end, it encourages laziness if someone has to wait to release something at a certain time -- "I have 3 months to finish this code").
Releasing beforehand also gives time for a smaller group of users to test drive code or whatnot that might have bugs, so that the bugs can be patched up by the time of the actual reunion when everyone is going to be downloading the code / mission / whatever. (See Plymouth Cold War -- I had to rush it to get it out by the reunion. As a result, the "AI" is perfectly horrible).
