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"I think some users are just so conditioned to the idea that CD burning is provided by a third party application that they don't even notice the integrated solution if it stares them right at their face."
These basic tools belong to Linux and BSD distributions for some years now. The users should get aware of the fact that a modern OS contains such tools by default.
"That cannot necessarily be fixed by the software, so why not tell them about it when they ask?"
Maybe it's too complicated for them to understand? "But I have to install something if I want to [insert desired action here]!" seems to be a common principle.
"Of course K3B is always a safe bet, but there is no reason to tell them to install K3B if all they want is to burn an image file."
For FreeBSD, burncd would be the first choice, connected to a drop icon in Gnome, or simply called via a xterm session.