I would disagree that blu-ray will only be 8-10 seconds longer than a DVD.
I would say blu-ray is about 4% longer than DVD.
Though that might only be PAL regions. NTSC regions might be different.
That only applies to PAL DVD which they speed up by 4.2% from 24fps to 25fps. This results in a 2 hour movie running about 5 mintues shorted on PAL DVD.