They don't send out a reinstallation DVD with the system. The idea is that the user is prompted to make media when they log into Windows.
Not all users do and sometimes creating the media/using the media does not work.
Requesting the media is too difficult outside the US in many cases; see this poll:
http://en.community.dell.com/support-forums/software-os/f/4677/t/19476992.aspx
For this reason I have began suggesting to supplement the recovery media with an Acronis Image, see Windows Reinstallation Guide and Related Wikies, section 3: