IMHO DVD-ROM is an obsoleted storage medium, USB memory sticks are much more flexible, reliable and portable. Furthermore a DVD player/burner require space, has an impact on battery and has a cost. That's why netbooks don't necessarily have to integrate a DVD player/burner. Actually there are only a couple of netbooks integrating DVD player/burner.
On the other hand we won't get rid of optical disks in the next couple of years (many of us got huge DVD/CD collections, printed magazines still distribute premium content using optical disks and many other reasons...)
A portable DVD burner with USB interface is very handy, especially if only USB bus powered. For this reason I prepared an Amazon bestseller list of external DVD burners.