Should I use a root namespace?

Question

I'm currently working on a couple projects in Flash ActionScript, and I've been building up a small library of classes. I've been using a naming convention similar to:

foo.events.Bar and foo.controls.Baz, but I've noticed that many people have released their libraries in the com and org package/namespace (i.e. com.foo.events.Bar and com.foo.controls.Baz). I assume the meaning of com is common or community, and that org is organization.

Is there a particular reason to adding an additional namespace?

Is this common for namespaced languages (Java, C#, AS3,...)?