Not as off topic as you think. Mumbai was never taken over - that incident is similar to Lahore. The state apparatus remains intact, elections are on, people go about their job and most importantly people remain unarmed.
A better comparison is Kashmir. The combined might of Pakistani cannonfire across the borders and the terrorists guns and bombs could not convince Indian Army to negotiate a treaty or to accede to Pakistani demands. The only thing that will change the status, if at all, will be peaceful negotiations.
What causes Pakistani Army to not be able to impose the constitution in Swat ? Why can't Army enter Buner which is halfway inside the territory (not a border area by any stretch)? How difficult is it to shut down an FM station ?
I don't think RAW is involved in this - if it is so easy to take over parts of Pakistan, India would be in Islamabad by now. No one in India has a mighty opinion of the RAW as Pakistan has. Even ex-RAW officials are writing books on the lost glory and de-fanging of RAW. Most of all RAW does not have access to stingers - and they were used against India in Kargil. How does TTP get hold of them ? And the best reason I have for RAW being not involved - If that was the case Pakistan Army would have moved much-much faster into Swat/Buner. Who wants to lose to India ?
I think it is a case of not facing the reality as muse is saying. Indian opinion is pretty close to what it is in the "open letter". New York Times is worried that Taliban is joining Punjabi militants and making a move down south into Punjab
http://www.nytimes.com/2009/04/14/world/asia/14punjab.html?scp=3&sq=pakistan&st=cse