There does need to be some regard to showing off Joomla when it is installed - not everyone is a hard nosed developer!
However, I also see the need for a very good developers template that really just has all the required code, a typography CSS (no values) a layout CSS - that sort of thing - and a bit of basic documentation to get people going.
The advantage of such a template being shipped as part of Joomla and being separate from the "Show off" template, is that it would be up to date.
You could have this as part of installation where you can choose a demonstration template along with the sample content.