Where'd They Get The Money?

The London non-bombings are of course the biggest story of today. My 2 X 2 bits:

1) Were these two car bombs supposed to go off? Or was it all a bit of theatre?

And most importantly:

2) Why were "they", whoever "they" might be, booby-trapping a couple of Mercedes?

Bombings are messages sent in blood and bone. What does it mean when you send your message of carnage via a luxury car?