This happened with 9/11, so there's no reason why this couldn't happen here.
The 9/11 terrorists were all imports, were they not? The 7/7 terrorists were natives.
AlQ wants to encourage Muslims in the West to become martyrs. What better way than to have some examples? Can't convince anyone to do it the first time? Well then at least make it look like they did it.
It is one thing to murder in the name of your religion, it is another to commit suicide in the process. Self-preservation is a pesky hinderance to such actions.
AlQ also wants to divide Western Muslims from the non-Muslims. What better way than to generate fear in non-Muslims of all Muslims?
I've seen nothing yet to convince me that these fellows knew they were commiting suicide. It's possible they did know, but I'm not convinced yet. Time will probably answer the question.