I had the same concern with a Dell PC that I recently helped the father in law to set up.
It doesn't come with a restore CD, but a piece of paper cut to "look like a CD" which explains that there's a restore function in the BIOS that will save the day following HDD failure.
Unless there is a chip onboard that contains a restorable image(?), then the only other thing that I can think of is that the BIOS restore function is dependant on you buying a new drive from Dell rather than some generic. Can't imagine that would be cheap?!
RC