Disclaimer: I am not a lawyer and this is not a legal advice. In fact, everything in here might be inaccurate and even wrong…

For the start: Everything you write down is automatically copyrighted and you have the absolute control about who can do what in which way with it.

Next, if you release source code and you actually want to allow others to use it in one form or another. That’s where the license comes into play, which range from the restrictive Just look, don’t use to the laid back Do (almost) whatever you want one. And, as the motivation for Sgt. Conker is to spread, share and increase the knowledge of the XNA Framework, this is the reason why all source code contributions to the site have to be licensed (the council prefers a lax one).

Lastly, why does The League of “absolutely fine” XNA Gentle(wo-)men reject code released to the Public Domain? To quote Sam Hocevar:

There is no such thing as “putting a work in the public domain”, you America-centered, Commonwealth-biased individual. Public domain varies with the jurisdictions, and it is in some places debatable whether someone who has not been dead for the last seventy years is entitled to put his own work in the public domain.

For example, as a German I cannot give up my copyright on anything I write (without inventing a time machine to die 70 years before I wrote it anyway) and the same rules apply – to some extend – to foreigners: you may be entitled to give up your rights in their entirely in your home nation (although even this common thinking is questioned) but as far as I am concerned you still have the exclusive rights to your code, rendering it unusable for me.

Post scriptum: Pages aiding in the choice of a license:

• HOWTO: Pick an open source license (part 1)
• Licenses on The Code Project
• Open Source Licenses by Category