Why doesn't X-Chat Aqua support MacOS X 10.2 or less?

This is because the perl plugin no longer works with the version of perl that comes with 10.2. Although X-Chat Aqua doesn't strictly rely on the perl plugin, it does use it to handle clickable URLs. I could have made a version for 10.2 that doesn't come with (or require) the perl plugin, but I didn't like the idea of releasing an xchat variant without the perl plugin. The final straw in this decision was that I wanted to take advantage of new features in 10.3. Future releases will make supporting 10.2 impossible.