Dell are currently shipping out most of their systems without reinstallation DVDs. For US customers there is an online request form for Reinstallation Media. For those customers not in the US you will need to contact Dell technical support and ask for one. The customer numbers are available here.
To improve the experience for customers from the rest of the world. Please vote on my idea Request a Reinstallation DVD form [Rest of the World]. Also see my poll here.
Thanks for the information