What evidence do you have to suggest interrogation has been successful?
From media accounts, they cite info given up by Al Qaeda leaders in interrogation. Some of the arrests of Al Qaeda members is said to have been the result of info from interrogations of their pals. There are also a few accounts of the US interrogators themselves who say that the Al Qaeda leaders are quicker to cut a deal for themselves than Abdul the Al Qaeda grunt.
Beyond the specific information above, I know from my brief experience teaching interrogation methods in AF survival school that untrained people break easily. They lack the intellectual structure to resist effectively. It's easy to trip them up. I also know that everyone breaks eventually if the interrogator has good enough info to know the right questions to ask and has good technique. The interrogator has all the cards and will eventually break any resister down, given months or years.
The only effective resistance technique to interrogation is to keep your mouth shut. Sounds simple, but hard to do. The fact that these Al Qaeda prisoners are talking at all, even to mouth off or brag, tells me that they have already lost the resistance battle and are in fact clueless in their resistance strategy. Once you get a guy talking, you have him.
And I think your claim that urban areas are hostile to terrorists (by which I assume you imply that such sites are difficult to hide in or operate in) is argued against by just about every present situation I can think of.
I disagree. Terrorists in urban areas are vulnerable. There is more security in a city, more ways to trace a terrorist act back to its perpetrators, more witnesses, more of everything that can undo a terrorist. You can't operate a terrorist organization in the long term in an urban area. That's why the Al Qaeda set up shop in Afghanistan rather than in Cairo or Riyadh.
If you examine equivalent historical situations, you can see the same thing. The French resistance in WWII was not particularly effective because the Gestapo simply ran them down with brutal effectiveness. Likewise, the guerrillas who assassinated Heydrich in Czechoslovakia in WWII were easily run down by the Nazis.
Castro based his guerrilla headquarters out in the inaccessible mountains. Mao took a Long March to hide out in the sticks. They did not set up shop downtown. It was too dangerous.
It's worth pointing out that Dr. Zawahiri, the No 2 man in Al Qaeda and the brains of the bunch, fled Egypt because he could not conduct terrorist ops from there. The Egyptian security was simply too good. They rounded up hundreds of the fundamentalist Muslim radicals fairly easily, executing the leaders and imprisoning the rest. He tried to set up shop in Chechnya, but the Russians caught him there and threw him in jail for a while to figure out what they caught. Zawahiri ended up in Afghanistan because they got chased out of all the preferred locations in the cities.
Lastly, you sentence "The authorities eventually run them down" seems to me to fail in the same sense that your BM analogy did. We aren't talking about a small finite group of individuals like the Weathermen. We are talking about something entirely different, surely. I recommend you switch to the Al Quaeda equals Communists metaphor.
America is doing quite a splendid job of running down Al Qaeda. We have captured half their leadership. That's pretty darned good for a year's work. It presents a depressing future for the remainder. And really, the more of them, the easier it is to catch them.