1) It's a little easier to make the list of changes for the release notes when the time comes.
2) Those who download the source and/or data from SVN get a more up-to-date assessment of what's been changed than looking at release notes, and a more concise list than the SVN log provides.
3) It's more convenient than checking Sourceforge's commit log -- which usually takes forever to load for me.
So, if there's no objection(s) i'll get it started. I've got the previous changelog entries in a document.
EDIT: for instance, i would write something like this for the work i've done since v.3.16. (I strongly recommend headings dividing it into logical categories, if not necessarily these exact headings.)
v0.3.16 + SVN
Graphics:
• Added binary star variant star graphics
• Added new building graphics
Ballancing:
• Decreased cost of colony pods by 25%
Species:
• Added a lot of minor "native" species, a few of which have extended descriptions.