Is the OS X Lion clean installation less stable than the upgrade install?
The DVD install is not an official, sanctioned by Apple, way to install the OS. So it's not that surprising that thing don't go as smoothly.  

Or maybe it's just bad luck when burning or installing the OS. So you can try to install it once again, even burning another DVD to see if that was the problem.

If you want to do a clean install, there will be official USB key in August. But they'll cost more that two times the price of Lion on the Mac App Store