To me when discussing testing I'm talking about software testing and there is nothing unusual or unnatural about testing on a copy of production data. In fact in my experience that is the norm.
Now in terms of content review and publishing yes there are systems that do it as you would like, but that involves a good deal more complexity. From a users point of view as long as content can be reviewed and approved I don't see where a multi server or multi installation architecture for publishing is to be considered always better. The vast majority of companies want simplicity and are not running sites on web farms and those are my primary targets. If some mega company wants to use mojoportal and they need this kind of formality of architecture they can sponsor development to get what they need or pursue other solutions. I certainly don't say mojoportal is the best solution for every situation, but its a damned good solution for most businesses.
If you'd like to build an API to deploy content in that fashion feel free, I'm not opposed to it but I think it will be challenging. Perhaps it should just be for the Html module to keep it simpler. Other features like blogs and forums it just doesn't seem to make sense for as the content often comes from the community and enters the system naturally through the production site. So definitely if using those you would want to sync from production to test or staging.
The main challenges as I see them are the fact that images are uploaded to the file system and the urls which are part of the content may be different for the dev and production environments unless you structure the staging site very similar. It does use releative urls for the html module, but the blog for example uses fully qualified urls because theyare needed for outbound rss feeds to correctly show them.
The other challenge that comes to mind is keeping the search index synchronized as it is also file system based.
These same issues also make mojoPortal not quite suitable for web farm deployment. I plan to implement a solution for web farm support but it will be an add on product and will not be free because it will reqwuire a lot of work and most people won't need it.
Best,
Joe