Isn't the point of nukes is that they cant be shot down. It's 2010 and the technology is just starting to go past the testing stage.
Actually the technology has been developed and proved since the 60'ies..
Sure, they interception rate can be discussed, especially as they where never needed, but they work in princippe. (one of the reasons nuclear subs where so interesting, no chance of intercepting those)
look for example at:
http://en.wikipedia.org/wiki/Anti-ballistic_missile
The reason for the lack of defence would rather be due to the "The Anti-Ballistic Missile Treaty of 1972" and the relative peace we have archieved due to the mutual destruction situation.
As the wiki states it:
"Technical difficulties aside, an odd anti-ABM argument developed: that no defense at all was better than any defense. Namely, a false sense of security might encourage ABM-defended nations to escalate against minor threats, believing they would be protected against any response. By this reasoning, simply starting to deploy such a system could prompt a full-scale attack before it could become operational and thereby render such an attack useless. This curious set of arguments implied that it couldn't possibly work, but if it did that would be even worse."