I read this question and was struck by something "obvious": why are not ICBMs built using "stealth" technology? A rocket, basically a pipe, must be much easier to "stealthify" than a irregular vessels like a plane or a ship.
Furthermore, according to the question above, the radar used to detect these missiles was using very low frequencies. AFAIK that means it wouldn't be good at detecting small objects. Compared to ships and planes an ICBM is quite small, making it even more motivated to build it stealthy.