> You need around 200 watt to hold 25kmph on a flat road
Most non-lycra cyclists I've observed seem to cruise at around 20km/hr; my personal experience is that 20km/hr is pretty easy once you're moving; 25 is a noticable bit more work. Also, for commuting where there are traffic lights involved (based on my own experience), you rarely have a chance to do more than 20, and if you do, any time advantage is killed by the next red light.
You need around 200 watt to hold 25kmph on a flat road without wind with a standard bicycle like the one in the video.
With moderate wind, it is between 350 and 400 watt.