Windows 10 will be shipped on USB drives rather than traditional DVDs, although you might be able to find one on DVD if you ask Microsoft very nicely.
USB versions of Windows 10 Home and 10 Pro are listed for pre-order on Amazon already, running $120 and $200 respectively.
It is all fairly obvious. Most cheap PCs ship without a drive these days which has made home-made USB installation drives the only option. We can still remember the outcry when people complained about the number of floppy disks it took to install Windows 95.
Windows 98 came out on a CD drive to cut down the numbers. Now it seems that DVDs are now going the way of the dodo too.