Actually, guided munitions like this do have moving parts (for fin deployment/actuation). The chassis could be made out of aluminum without being too heavy, though I'll agree that optical drives and LCD are probably the big limiting factors for the computer. (And I'm guessing that economic feasibility is another big issue).
FWIW, I have worked as an engineer on similar projectile projects, but have not been involved in laptop design, so I must admit that the Dell engineers probably know more about it than I do.