True, they probably will... BUT they don't always. I once booked two J returns LHR - SYD on BA, on an Amex 241, and they never deducted the Miles. Unfortunately (no, MEGA unfortunately), I had to cancel the trip as my girlfriend and I went our seperate ways - but 10 months after the booking had been made the Miles had still not been deducted.
Sadly they didnt credit my account with "bonus miles" at the cancellation... But I'm pretty adamant that had I flown, they would have been totally "free" flights...