Most likely more... The ED visa is less flexible than the DTV. Leaving the country for a few weeks for business or private reasons is much easier on a DTV, you go, with no planning, and a re-entry permit isn't required.
You can't just leave for a month on an ED visa, at least not at the school I have enquired about.
I'm not saying the DTV is the better choice, it could be but it seems Immigration doesn't like the DTV all too much.
Most people holding a DTV won't do an extension, less work and control, and mostly less income for the Bureau.