At the risk of the FBI stashing a tracking beacon in my car (ha! I don't even have a car!) I'm going to take your bait.
Richard Reid's bomb didn't fail because he had to hide it in his shoe, rather than doing the ol' Ramzi Yousef "hide it in the life jacket routine." Umar Farouk Abdulmutallab didn't fail because he had explosives shoved down his shorts.
They failed because they were untrained. These guys displayed a Carlos the Jackal level of buffoonery in their conduct. The July 21nd attackers didn't fail because of the crack police work that went on to murder Jean Charles de Menezes. They failed because they were too stupid to build bombs. (Who would want to target Hackney anyway? It's just a bunch of tyre shops and fish & chips.)
For the most part, people who want to do us harm aren't particularly smart. Bright people tend to have more opportunities in life and are less to see that all go up in a puff of smoke. Of the 9/11 hijackers, only one had a girlfriend. Atta was a trained architect, but for the most part they were a bunch of college dropouts. We aren't faced with some "evil people somewhere insidiously committing evil deeds," we're faced with a bunch of bumbling fools with nothing better to do than kill themselves.
Look at the Aum Shinrikyo sarin attack. They had a deadly neurotoxin that they saw fit to unleash with pointy umbrellas and newspaper rolls. Good job team, way to unleash your crazy new age apocalypse.
It isn't a matter of loopholes getting closed. Attackers are simply dumb. Really dumb.